Take on the duties of a Knight-errant in Toussaint.
The Witcher 3: Blood and Wine - Knight for Hire
This quest is found on the noticeboard at the Cockatrice Inn, the Inn you're forced to visit early in Blood and Wine after battling the giant and investigating the bloody scene by the shore. It can be undertaken as soon as you gain free control of Geralt in Toussaint.
Start off by following the quest marker to the Ducal Camerlengo - which is the big old city-looking area central to the world. In the city proper you'll find a small building, as pointed to by your waypoint - inside, talk to the fellow there and after some chit-chat you'll be given fifteen contracts to take care of spread out across Toussaint.
These contracts are a great way to get to know the terrain of Toussaint if you're early on in Blood and Wine, as they're spread far and wide across the map, meaning a lot of travel to discover points of interest and the like between points.
Each of the fifteen points of interest is one of the typical Witcher tasks Geralt so often undertakes - some are Abandoned places that have been infested by monsters, some are monster nests, and so on. The tasks pretty much always amount to a bit of combat and perhaps a bit of searching on the side after slaying monsters and destroying their nests. All these tasks are really simple - so get to killing!
You don't have to do these fifteen locations all in one go - you can also happily leave them and attack them only when you pass nearby, if you want to avoid all that travel. The upshot is that when you return to the quest giver, he'll compensate with you for some coin for your efforts for each and every one of the locations you clear out.