The instructions are explained in game, although I'll explain it here as well. ↑ to go forwards, ↓ to go backwards, ← to go left, and → to go right. Z to do an ollie, (a jump with the skateboard) and ↓ while pressing Z to do a kickflip (kicking the skateboard mid-air so it flips a full turn). I'll add more tricks and make a league mode soon (after the holidays).
I actually don't know who to give the credits to so I'll just say thanks to the scratch team. When you are pressing ↑, it's normal to go down instead. Just keep your finger held on the key. When you are doing tricks it might delay a bit or not do anything at all. Just try again. I actually skate and I can guarantee you that it's not as easy as this. As normal, just let me know if there are any bugs. Also sorry the skateboard is so small. Update log: 0.1: Game released 0.2: Added this update log, home page, AI page, and changed skateboard look 0.3: Added man to skateboard and fixed turning bug