Hey,
I have a guide here on steemit about getting started in crypto Getting Started Guide
I started by signing up to Coinbase and then Kucoin and I keep signing up to new exchanges depending on the coin I am after. I think its good to be on as many exchanges as you can so you don't miss out on any altcoins. Also having your investments spread over multiple exchanges means you are less likely to lose all your money if one gets hacked.