APEX & Strike Teams is a peripheral activity that’s completely optional and, for the most part, unrelated to Priority Ops, although it ties into Multiplayer aspects. For Single-Player purposes, it’s largely a “set it and forget it” resource, providing bonus rewards like credits and minerals.
You can have several strike teams. The more you have available, the more missions you can undertake at once. Recruit strike teams by spending mission funds through the teams menu and equipping them.
Strike teams can earn positive and negative traits, depending on whether they succeed or fail on their deployed missions.