Some scenarios require mods. I would first either pick scenarios that don’t need mods or need only a few. Mods are subscribed to the same way but you enable them in the Arma 3 launcher, and they will take effect in all scenarios when you have them enabled.
The quality of scenarios varies widely, but the popular ones are usually pretty good.
How do you get into the game modes? I played all the campaign and there’s nothing left
You can play Scenarios (missions) by following these directions: https://arma3.com/workshop101
Some scenarios require mods. I would first either pick scenarios that don’t need mods or need only a few. Mods are subscribed to the same way but you enable them in the Arma 3 launcher, and they will take effect in all scenarios when you have them enabled.
The quality of scenarios varies widely, but the popular ones are usually pretty good.