2 players - Garden warfare

I don't believe PC supports split screen coop. 

If you wish to play with a friend:

Join a match, have your friend right click your name in origin and join or you can right click their name through the origin overlay (shirt + F1) and invite them

You can create or join a Garden Ops match and an invite option will be available in the lobby. If you're in a game, you can repeat the step above