This cast-on is simple and often used to add stitches at the end of a row.
At the end of the row, pick the working yarn in your left end. Create a loop around your thumb with the yarn going in front, then above, then below your thumb(then to the needle).
Pass the point of the needle in the loop, from below.
Release the loop from your thumb (but leaving it on the needle).
Tighten the yarn around the needle, close to the previous stitches. You cast-on 1 stitch.
Repeat steps 1 and 2 as many times as necessary until you have the desired number of stitches (here, 10 stitches).