You get missions from your contacts. You access your contacts via the ST combadge logo on the UI (left of the mini-map). Click on that and you can get a list of current contacts. They'll give you missions to do.
Also, the game has always had episodes. Those are the missions that aren't patrols. If you mean Weeklies, you have to be Lt 6 or higher to start the Devidian Weekly and Lt 10 or higher to do the Defari Weekly series.