You're a little confused which is not hard considering they explain fucking zip.
"Jobs" are the name for basic gameplay modes, Deathmatch, Race etc. This also includes "Missions" which are effectively deathmatch with lite objective flavouring applied,
The Co-Op content I think you are after is given by Mission givers, Simeon, Lamar, Gerald etc. These appear randomly via text and once you reach a high enough level you can request them. You launch them and have the option to invite friends, crew mates or players in your current "server"
Its got such a awful UI doing much of this is a nightmare. Even when you get past the bug ridden intro it feels very much like a beta.
I had some shallow fun in a private server last night with a group of 4 of us and we managed to do one mission which was recover drugs from a lost + vargo trade. Its incredibly simple stuff shoot 10 AI and then drive back round the corner.
Nothing feels polished, the character creator is a joke. Even when the issues are balanced out it seems like to much focus on PvP.