So I was messing about with some of the key bindings, trying to find what's comfortable, when I came to the "slope-running" section of the tutorial where it just said to hold down the "Right Mouse button" and didn't tell me what the Right Mouse button was supposed to even do. At this point I had changed RMB several times and now have no idea what action RMB is supposed to do?

In order to sloperun you have to use "+cmd_special" bind.

If you want to use Right Mouse Button to perform sloperuns type "/bind mouse2 +cmd_special" in console (you can open it using ESC button), and then press Enter.

At the timestamp in the video you can see what sloperunning is about.

When you approach the ramp, and hold down button with +cmd_special bound to it, you can slide upwards/downwards it. If you slide on the ramp long enough (300ms+?) you can press Jump button, which will trigger Sloperun Jump, launching you relatively high into the air.

Amazing, thank you! yeah all I needed to know was what the action was called. Thanks!