Today’s free update for Grand Theft Auto V adds new capture-the-flag game modes. These are called “jobs”, which I presume explains why you get money for doing them. Not to mention “job points”. And these are no mere flags, which is why the modes aren’t technically called “capture-the-flag”. Instead, they are raid, hold, grand theft auto, and contend. Read the details about each mode here.
Or, heck, just jump online and start playing without having any idea what you’re supposed to do. It’s worked for me. I didn’t get my online character to level 12 by reading rules.