To start, go to: https://codecombat.com/
and sign up to the site. There are lots of levels to try out, and as you go you will gain more powers and better equipment, but don’t worry there is a good introduction to them all as you go through the levels.
As you get further through the levels you will also get tutorials on creating you own levels and an HTML wanted poster.
Some of the later levels involve some interesting challenges, and there are online competitions if you want to try out your programs against others.