New here. Need help

Yes, food can affect a horses behaviour a lot. Some horses can't eat oats without being a bit crazy.. just as an example. Barley can give a stoach ache if it's given too much and who wuldn't be annoyed and irritated with a bad stomach? We have to remember that horses are made to eat grass, not grain. But when we keep them, some horses need more than hay to keep their weight and that's where grain and other horse food comes in. Like my horse; he gets 10kg hay, which isn't much but it's all he manages to eat) and since that's not enough for him, we need to give him a kg barley too. That's the only thing I've tried that works. Our other horse gets fat on only 5kg of the same hay.. so it's individual :3
Another thing is that horses should always have hay or straw or grass to eat their stomachs doesn't work like ours and when they're empty there's drippin acids into them. It's supposed to take care of the food, but when there is none it's burning the insides instead and can give ulcers. (with humans, thse acid only come when we have eaten). Some investigation I read said that 80% of horses standing on something else than straw, and without free access to hay, had ulcers when they died.
So food matters a lot with the behaviour :)

A square ''roundpen'' will work better if you can cut the corners somehow, and if it's not too big. You need to know how to work in a roundpen too and what to listen/look for in the horse while you work. :) O key rule to all horse handeling; the horse should never be scared or in pain.

You can excercise without riding or lunging (I personally don't like lunging), with long reining, walks, working in hand or why not just try to get them used to new, weird things (gabage bins and chairs can be really weird for a green horse :P) that also helps making them ''bomb proof''. Of course they can be pasture pets, but the risk is that they'll ''forget' things they have learnt when you handle them, easily get spooked when you do decide to ride or just starts behaving bad as soon as you ask something more of them that to lead them to the pasture and back. Some horses can rest for a week without showing any differense, some gets excited and topped after a day. The young horse definetly need some activation and handeling.

The correction thing; learn to listen to your horse, he gives you rather a lot signals before he becomes too bad. It can be to take a step forward, wrinkle his mussle or turn an ear. But the signals is there. And, as long as the bad behaviour is on a smaller level (stepping around or just being annoying) give him warnings first. It can be to just clear your throat or glare at him while saying ''hey!'' or ''no!'' in a low, ''dangerous'' voice. If he stops, even if it's just for a few moments, everything is okay and you must be happy again. This is important. When he starts again, you give him the same warning. If he doesn't listen at all, you go through with the warnng and slap him on the butt or shoulder, or wherever you reach except the head. If he moves away or jumps away from you, that's also ok (that's what you told him to) but once he has done that he should be calm, and you should be happy again.
If he kicks or bites tho, just skip the warning. That's something he knows is bad. But remember to always be happy the second he behaves.

How much time you should spend with them depends.. the matter is; how good is the time you spend with them? ;) Some days I just clean the stalls and feed and spend no time at all. But if you want to solve a problem, or improve something, you should spend more time with them. It's better to train them fr a short while (10-20 minutes) several times a day, than to demand their focus on you for an hour or more.

And about the treats... the horse doesn't need treats. They of course likes them, but it's ratherunatural for a horse to give or recieve treats, so they don't recognize it as you bing nice to them. At most they recognize that you have treats, and then they start to beg for it, and gets annoyed when they don't get it.
It's far better to create a bond by rubbing his favourite spots (withers is usually a lovely place but you have to find that yourself. When he relaxes and his muzzle starts to move, you know you've found the perfect place :P ) and to be a good leader. If he knows what to expect from you, he is much calmer and gets a better confidence.

I hope I'm not sounding like I talk to a child or somthing, I'm just trying to be clear.. :3 It's not so easy when I onlty know half of the words I want to know x)

I would suggest you find a trainer that will come and work with you and your horse. You both need some training . He is just being a brat, a young silly boy. He needs firm leadership and very consistent handling. Young horses are generally not a good idea for first time owners. They are quite demanding and training can be time consuming. But, if you work closely with a trainer, he/she can show you how to overcome these issues now, and WHEN they come up again.

A horse is not physically mature until 5-6 years old, and boys can mentally mature as late as 8-10 years old (though 5-7 is average). SO, you have a LONG road a head of you . If you nip this behavior in the bud now, things will go a lot smoother up ahead.

As for his feed, food issues can cause aggression (both what they eat and how they behave during feeding time). I would have him brought in everyday for his grain. I would also not feed him traditional sweet feed. It can cause negative behavior in some horses (think of a kid on a sugar/caffeine high). I would switch him over to a ration balancer like Purina Enrich or Triple Crown's 30% supplement. Weigh out 1 pound and feed that to him twice daily (or whatever the bag recommends for a horse his age).

Along with that, give him some Alfalfa or Alfalfa/Bermuda hay pellets (3-5 lbs) and a fat supplement, like corn oil, flax seeds, or rice bran. Feed up to 1 cup of oil, 2 cups of flax seeds (whole), or 2 lbs of rice bran.

Switch feeds slowly, over a 2 week period. You don't want to change his diet suddenly.

Keep giving him the same hay. As the pasture grass dies off, make sure your boarding facility is putting hay out for the horses in their paddocks/pasture.

He should gain weight slowly on the above diet, and grow. He will continue to grow and fill out until around 5 yrs old. Young horses often go through "skinny" phases where they grow up faster than they grow out. This is normal.

One more thing, have you been deworming them? If not, I would give them all a double dose of Pyrantel paste (the active ingredient) now and a regular dose of Ivermectin in 4 weeks. Then get them on a good schedule. Avoid using products that contain Fenbendazole or Oxibendazole as they are not effective in a single dose. I rotate between Pyrantel, Ivermectin, and Moxidectin with at least one deworming a year of a product containing Praziquantel (to get tape worms). I always use Pyrantel in a double dose as it's more effective that way and will get some tape worms.

I use the web site http://www.redndaivu.com to help keep up with my deworming schedule (and farrier visits, vet visits, etc.). It's a free online horse tracking software. It's very handy!

Treats are fine, but only if they earn it and will take them nicely. I use treat time as a training exercise. It can be very helpful!

Maybe it's just not a good idea when you already have this kind of problems? :) Timing is so very important when you use treats for training, and also quite hard to get right, especially if you're not very experienced and hasn't learnt to read horses completely yet.