This tutorial deals with WebGL 1.0. It is about displaying your first triangle using WebGL and knowing what the heck is going on in that blob of code.
Please be warned that there is a lot to do before you will display it, so don't be cocky and take your time to understand every step. Eventually you will get there.
Good news is that after displaying first triangle, all the rest is relatively simple.
I will be explaining everything, but some things only cursorily. The point here is to understand how to make a triangle and build foundations for further learning, not to display it as quick as possible.
I wrote this tutorial because I felt like there is no small-step-based introduction to WebGL and its needed. Enjoy!