Here are some other online resources for learning about special relativity
The one must see video, that best explains space time diagrams and special relativity is from the "PBS Space Time" Youtube channel "The Geometry of Causality | Space Time" . The video succinctly explains what a space time diagram is, how it works and presents an interesting interpretation of what it shows. In addition to that video is their playlist "Intro To General Raltivity" where they go into more depth.
Another great Youtube channel is Fermilab, they have a "Special Relativity" playlist, presented Dr. Don Lincoln, which is pretty good. That is, if you can survive his really bad jokes.
Finally there are the videos from Minute Physics, specifically their "Intro Special Relativity Course" . The video's that inspired this website. This series is great if you just want an overview, but I find it leaves you with more questions than answers.