I found these following resources incredibly helpful amongst a swathe of confusing guides on the web. These are good places to start if you know very little about skateboards and RC (Radio Control) components, I learnt from these links.
How to apply grip tape.
Never knew skateboards has a tail and a nose. Nose is longer, use tape measure to determine. video.
Wheels and bearings: video and another video.
Calculating speed: link.
Understanding batteries: link.
Connecting batteries and esc: video.
Ask for help on forums, learn from others: link.