How many fish per gallon? How dose this work .

Hello everyone. I am very new to the fish keeping hobby . Never in my life Owen a fish take let alone . I just bought a 120 Gallon set up waiting for shipment. I have been doing a lot of research and seem to know what I'm getting into. But.. would like to know how many fish you can keep in 120 gallon tank comfortable. Don't judge lol just new to the game .