You get credits that can be invested for multiplayer progress by playing against bots. You get 100 credits/match played against bots (whether you lose or win that match is irrelevant). The amount of credits you can earn from playing against bots is limited to 500 credits/day, so you only get rewarded for playing 5 matches against bots.

What people here don't tell you is that you can get these credits by playing a custom arcade game, you can make a game that is just "kill 5 enemies" and you're done with it in 15 seconds. So you can basically earn 500 credits/day just by logging in, playing against bots for 3 minutes and logging off again.

Playing against bots is obviously not meant to let you progress in multiplayer, it's more like an daily encouragement to start up the game to earn some easy credits in the hope that you'll end up playing multiplayer aswell when the game is already running.