The section of the Potomac River from Point of Rocks to Brunswick is undeveloped and very scenic. The river is fairly wide, relatively shallow and rocky in places, with a moderate current. Most folks choose to float downstream, but a reasonably fit paddler can go upstream and float back down. Solo canoeists will want to have a bent shaft paddle or a kayak paddle for the upstream leg. Certain sections of the river are popular with fishermen, but it's a big enough river that there is room for everyone. There are a couple of spots that require a basic ability to read a river and pick the proper line. Life jackets are required at all locations.
Some camping at various locations in the C&O Canal park.
No fees required on the Virginia side of the river at Point of Rocks. Not sure about the other launch sites.
Take route 15 to the Potomac River at Point of Rocks, Maryland. If launching from Brunswick and coming from I-70, take 340 to route 17. Take 17 south to Brunswick. 17 goes to the river. If coming from the Virginia side, take 287 north from Lovetttsville. It will turn into route 17 when you get to the Maryland side of the river.
At Point of Rocks, the public launch area on the Virginia side is the first road on the north side of route 15, and is clearly marked. There is a public launch area on the Maryland side as well. It is off of the first turnoff on the Maryland side of the river. In Brunswick, the two launch areas are located in the C&O Historical Park, which runs along the Maryland shore of the river on the downstream side of route 17.
If you feel that you need better directions, the ADC map for Frederick County, Maryland shows all of the roads and launch areas.