Favours are tasks that you complete for other inmates. Inmates who have a favour to complete have a green exclamation mark (!) above their heads. Press A to interact with one of these guys and accept their request.
Favours range from beating people up, delivering items to guards or other inmates or crafting items.
Once you have a favour to complete, the items or person to go to are indicated on the map as a yellow pin on a green circle.
Complete 100 of these favours to unlock this achievement.
Note: where you need to collect items, you need to collect a specific item from a specific location. It’s no good if you’ve already got the item in your inventory - you need to obtain it from the location specified.
You can have six active favours in your journal and you can select each one in there to make it your ‘active’ favour.
You can do this on centre perks 2.0 as there are lots of favours on the go and the daily routine is quite relaxed.