A maker fee is paid when you create ("make") liquidity on the order book, i.e. you create an order which is not matched immediately.
A taker fee is paid when you remove ("take") liquidity from the order book, i.e. you create an order which matches an existing order (this includes all market orders).
Your 30-day trailing volume which impacts your fee rates.
Your fee tier is based upon total USD trading volume over the trailing 30 day period.
See
https://help.coinbase.com/en/pro/trading-and-funding/trading-rules-and-fees/fees.html