OK, this is a pretty simple game. You're a cute fluffy wuffy little dog out in the park to play catch ball, frisbee etc. All you need to do is jump up to catch various objects, but be very careful, there are certain things like grenades you definitely don't want to catch.
Sound easy enough? Well I'm sure you'll know soon enough.
Use your mouse to move dog left or right. Left mouse button to jump. Hold mouse button down for longer to increase jumping power.