Codex entry
In the overview panel, which you can show or hide using 
you will see the current objectives for the selected quest. You can read more information on the quest in the Journal using 
which on the righthand side toggles between the map and a detailed walkthrough of the quest.
By pressing 
you can choose which of the non-completed quests you want to pursue. You can pursue a maximum of three at any time. After launching the quest, a coloured shield will be assigned to it, which on the map and on the compass shows the waypoints for completing the various objectives in the quest. The place shown on the map maybe a specific point or an area. For convenience, the various objectives are labelled with letters.
If you want to know what's going on in the vicinity or find out if anyone needs your help, it's best to ask the local innkeeper, who's sure to know all the local gossip.