I'm not from the US, but that shouldn't matter.
when I first started I went to the local hardware store where they have those racks full of 2-5 dollar stuff.
They usually contain locks as well, easy locks.
Then you also have the locks where there are a couple of locks in one package for a few dollars, these are easy to do as well (perhaps too easy, but at least it'll boost your confidence

).
Just get some cheap locks, the cheaper the better to start with (make sure they are pin tumbler locks though).
After a while you can start with branded locks (Master, American Lock, Yale, ABUS, etc) these will have cheap locks as well as high security locks.
The Master #3 for example is a lock which is really easy to pick, The Master #540D is a Maximum Security dimple lock which is a lot harder.
Then there's a whole range of locks in between those as well.
Most brands have ranges like that.
Just remember, the cheaper the lock, the easier the lock
