The trading platform or the exchange is where you have your money and where the bot make trades on your behalf.
Binance
My recommendation and the biggest exchange with the most options.
Free to register and low fees to use.
Even that this is the exchange with the most features it is very easy to use.
Bybit
Very large exchange with “Free trading available”
Many options.
Free to register and free trading available.
Poloniex
Very large exchange with “Free trading available”
Many options.
Free to register and free trading available.
A complete list of exchanges to be found HERE