[turvas]

There are 2 main ways of doing this. One is raster and the other one is vector.
For vector you just make the shapes and etc with pen tool, kinda easy when you have been using the program for a long time.
The raster way would be: Pick the brush tool and select a solid round brush with the size you would want the curve to be at it's widest point. Then pick the pen tool, then select path mode (not shape mode), and make a kinda curvy line. Then right click and select stroke path, select Brush tool from the drop-down list and be sure to check 'add pressure' or how ever that option a bit down of the list is called. Have fun.