select a server in the "PLAY" tab and press join
when in game jump on the ramp and use A or D while moving ur mouse

**for example if ur going right u press D, If ur going left u press A**
when u learn that u can combine W and S to strafe sideways in air.
for example if ur in air move ur mouse to the right and press W to strafe sideways-right, and to strafe sideways-left u move ur mouse to the left while pressing S!

hope this helps :3