Drawing basic shapes can be done with the shape tool and can be modified if needed .
the pencil tool allows you to create freeform lines, the pen tool an create shapes or be used to trace images.
complex paths require you to hold shit and curve the line you made.
you can reshape shapes and you can create curves and tight edges.
if you mess up a path you can erase them and go back with the smooth eraser and path eraser.
Alejandro’s blog 