Another achievement you will achieve as you progress in the game. Before the Orphan quest, you receive little main quests, so the side quests which are known as 'Unimportant Things I Need To Do' will be your main stay for most of the beginning. Although these quests aren't required, they're recommended since you'll get a lot of experience if you do them, and you'll need the experience to reach level 20.
The main thing you should remember though, is that you have to turn them in to completely finish a quest. Any quests that need to be turned in will be highlighted green in your Quest Log.