Side missions are found from the boards in the safe houses of each area including the Base of Operations. Locating these in your map will activate them and give you a spoken mission brief from the areas mission co-ordinator that you find in each areas sage house. The briefs and subsequent progress updates as you move through the mission are often made amusing by the personality of each mission co-ordinator. From adoring fan to wannabe actor and more these individual co-ordinators do make the missions a little more interesting.
The missions break down into various types.
Kill a specific names enemy. This will mean approaching a guarded location and working your way through several areas of enemies before reaching your main goal. The areas will have higher level lieutenants that you will need to deal with first.
This is a times mission, the timer will start when you activate the first switch. You will need to complete several tasks including activating panels or starting generators to get the communication equipment working again. Your progress towards each objective will be hindered by enemies so you will need to take them out quickly. There should be plenty of time to deal with the various objectives unless you get lost finding your way to the next one.
Mission person missions involve travelling to points on the map to investigate Evidence in the form of ECHO playbacks. These are multi-part missions which the completion of one echo leading to the location of the next. You will possibly encounter enemies on the way to or at the echo locations so be prepared to clear them out. Some missing persons are found in unusual circumstances.