Vang_Vieng is a town in Laos.It is a popular tourist destination - expect a lot of backpackers, tour agencies and hostels/guesthouses.
Inside of the town there is no need, your feet will take you everywhere within a few minutes. Heading to the Blue Lagoon+caves, this road is hitchable. There are two bridges in town - the northern one is for free (pedestrians/bikes only) and the southern one is charged. Walk across the northern bridge and south along the river until you get to the end of the southern bridge. You can start walking towards the west and along the way flag down cars, pick ups and bikes.
North towards Luang Prabang
There is no difficulty. Walk to the main road, let someone take you a little further outside of the city center (2km sign) and start hitching.