Each faction which offers a job (except Mercenaries) can offer taking over outposts as well. This type of mission is about reaching marked venezuelan bases, killing soldiers (not necessarily all of them) and calling backup for free.
When you do this helicopter will reach your destination (if not that means too many active anti-aircraft devices are still nearby) and drop off a few soldiers. Xs into the upper right corner [#168] inform how many allied soldiers have to enter outpost to take it over.
For instance, if there are three Xs that means three soldiers must enter the building; but you mustn't allow other enemy soldiers to get into that post. If the building enter two allied soldiers (when three are required) and after that two enemy troops as well, ratio between enemies and allies will be equal. That means you still have to send tree soldiers to get into that outposts.
Allies arrive in a helicopter [#169]. Your job is to make good conditions for that; just neutralize anti-aircraft devices.
Each outpost has an alarm system. If rival soldiers manage to reach turret with installed siren they will start alarm. After that near buildings will become a big problem. Soldiers will use windows to shoot you down (with RPGs). Unfortunately, it is impossible to kill all of them - their number is without limit. The best way to solve that problem is to demolish enemies' barrack or destroy sirens.
Your opponents have heavy vehicles (e.g. tanks). You can steal that machines [#170] and use them against you enemies.
Prices for outposts are the same in a particular faction.
Taking over outposts is very important. Thanks to that you will get money but also you will unlock missions (connected with storyline). Moreover, each conquered post will become a point where Ewan can take you.