Sky Roller is a skating game which is a bit weird in that it is quite far from anything you could consider to be realistic and takes us through an abstract world, fairly common in casual video games, where we will have to put our skates on and skate along impossible tracks avoiding obstacles.
Slide your finger to open and close legs to avoid obstacles
To progress all you have to do is slide your finger left and right to open and close the legs of your skater in order to avoid the obstacles along the track: sometimes there will be blocks in the way and other times precipices... but you can also collect diamonds as you skate in order to get more points. These diamonds can be used to customize your skater with different skins.
As is usually the case in a good casual game the only objective here is to keep progressing in the game to while away some time. There is no finish line to reach and no other purpose than to kill time.