You will go through a period of "figuring out" your new horse. And your horse will have to figure you out too! While most cues have a general rule of thumb, there are slight variations.
That is good that you already have a trainer coming to help you. Hands-on learning is the best type of learning, IMO.
can you tell me how exactly to "send" her through a gate, and possibly how to ask her to "wait"?
It has to do with your body placement in relation to hers.
If you step back to "open the door", and point with your arm (the arm away from her), that typically is the cue to send. Make sure you have your chest pointing where you want the horse to go (but not so much so that you have your back to the horse).
Likewise, if you want to stop her body motion or make her wait, angle your body so your chest is pointing at her shoulder to "block" her forward movement. You could also put your arm/hand in front of her to "block".
Most of it is just learning what affect your body language has on her, and how you can use your body language to control her shoulders, ribcage, and hindquarters. You'll get it wrong in the beginning, and that's okay! You'll learn with practice.
This is a post of mine I wrote up a while ago. https://www.horseforum.com/horse-trai...-101-a-205770/
Yes, the title is trailer loading but really, trailer loading is about ground work too. Might give you some ideas, anyway!
You could also look up some ground work videos by Clinton Anderson. Now, he's much more aggressive in his cues than most people need to be, but what I like about him is he makes his cues very obvious and he explains what he is doing, when and why. So you can see how your body language causes the horse to move in relation to it.