What do you mean by curves? Just brush work? Because if so, you can go to the brush creation tool and you should see this little box wherever you have it on your screen.
It should just say: 'block' at first, but you change this to the 'arch' brush and you'll be almost all set.
Wall width is how large the brush will be from the outside inwards.
Number of sides, pretty obvious.
Arc will change the shape by being a certain angle. (I prefer to make a full 360 and multiply the number I need by 4 so I can cut it down)
Start Angle will change the direction it starts at.