I wanna be able to know how much my opponents have in their stacks. whats the best way to learn to be able to know how much they got? should I count stacks at home with chips and try and count it from across the table?

It's just basic maths. Extremely basic eight year old level maths. If you can't see that he's got two 20 chip stacks of 500's and know it's 20k straight away then just ask for a count

First learn the denominations by color. This can vary some from room to room! Then try stacking at home at the right distances you will be looking at. Over time it will become easier. BTW in most cases you will not really need an exact count to make your descisions.

So, first to clarify the most common rule. You are entitled to a count of a bet, you are not entitled to a count of a players stack. So, if he goes all in, you can ask the dealer to count his stack. If you are considering going all-in and want to know how much your opponent is playing, you are only entitled to a clear view of his chips. Now most players and dealers will give you at least an approximate count if you ask (as a player, if someone asks what I have, I just make sure my stacks are all visible).

As far as learning to sight count, practice, practice, practice. When not in a hand, practice on the guys one or two seats away from, you, where you have the clearest view. Learn how to recognize stacks of 10 and stacks of twenty. learn to tell if it looks like there are stacks behind the visible stacks.