hi! I don't know about learning how to trade stocks but I don't think that you can trade them for free. It might be different in the US but here in Canada, (at least the bank/website we use) you pay per trade and to get cheaper rates, you have to do lots of trades every month or every quarter.
I don't know if there are sites where you can PRETEND to trade. Did you google it? Also, whenever you buy or sell stock you can lose (or gain!) money, so it's not really something to just play around with imho.
Good luck learning. It feels great to have control of your own investments.