Yep get a trainer!! You won't get extensions for a few years yet, like what you see at FEI level, but you can lengthen the paces to a medium trot/canter. Walk is a different matter, extended walk is a difficult movement, you don't need it until you reach the upper levels of dressage. The only walk you will need in what you will be doing if you start competing, is medium walk (which is the equivalent of working trot and canter) where the horse is round, over its back has a good contact on the bit and is marching forward with a clear 4 beat rythem. The other is the long rein walk, which is mainly used to cross the diagonal and change rein in a test. Again, the horse should be going actively forward in a clear 4 beat rythem, but the neck should be lengthened with the ears level with or lower than the withers, but not on the forehand, the back still needs to be round with engaged hindquarters.
There is also collected walk but again, this is not needed for some time.
As ridergirl said, get yourself a good trainer that can help you. If you already have a trainer and she hasn't started you on lengthenings yet, that is probably an indication that you are your horse aren't ready for them at this stage. The horse needs to be engaged, have good balance, rythem and straightness in all 3 gaits before you attempt a true lengthening, and even then most horses lose their balance for the few attempts, most will break into canter from a lengthened trot, so you want to ask for only a few strides at a time, then bring them back for a few strides, then out again for a few, just to build their confidence and stregnth.