You need an exchange that's active in listing new tokens/coins and it's left for you to research on which token/coins is worth trading also try trading coins with low supply as I consider coins with huge supplies to be a long term investment projects considering the project is worth investing in.
OP can stick to the most reputable trading platform for now. Since OP is confused on what to do, the best way is to minimize the risks he is dealing with any exchanges so Binance as an example will be a good choice.
And it might difficult if OP will consider trading on low supply coins or low market cap today since he is still on the learning process. I suggest to just stick with Bitcoin or any top currencies for the moment so that while learning other things, he isn't increasing the risks of losing much on other altcoins.
Step by step and hopefully he will learn someday.