Like the previous guy said, push X and check your skills.
If you have at least 1 point in the Riding skill - walk up to your pet and push R to ride it (list of rideable pets: http://cubeworld.gamepedia.com/Mount_Pets)
If you have at least 1 point in the Hang Gliding skill - equip the Hand Glider and then push G. While gliding hold Spacebar to keep your altitude and boost your speed a little though careful - your Stamina will quickly drain!
For pets, you have to keep up their stamina up to ride them. Stamina is indicated by the bubbles under their exp bar. To fill their stamina you have to dip them in water to let them drink. --- Wii U: Pikmin 3, Watch_Dogs, Super Smash, Mario Kart 8, "X", Bayonetta 2 PC: Assassin's Creed IV, Titanfall, The Witcher 3, Transistor, Battlefield 4