We like Coinbase as an easy way to get into this. They sell the 3 major coins and say they will be adding more. Go to Coinbase to get your first Bitcoin, Etherum, or Litecoin and then you can transfer it to an exchange and start trading it with other coins. I have been using Binance and am happy so far. They seem to have the lowest fees. Please use my links because they give us free stuff if you do. The Coinbase link gives you a free 10 bucks. This is great because it covers all of your fees.
This video is very good at explaining how to take the coins you purchased at Coinbase and using them to buy other coins on Binance.