• You die from three hit in this game. Your hit-box is extremely small. When a bullet spawns for a split second its hit-box is a radius around the player, providing a sort of "shield". Your screen will shake slightly if a bullet is used up this way. You will get hit if there are too many enemies coming too fast for your fire rate to handle.

• The green things that drop from enemies are shards, collect them for points. When you jump they will move to your vertical position, but not horizontal.

• You can jump off of enemies. An indicator for when you can jump will appear both under the reticle and on your gun.

• The purple things are bombs, touch them to make them explode and kill a bunch of enemies. Shoot them to make them slowly move towards you. Exploding a bomb will restore 1/3 of a life.

• There can only be 3 bombs at any given time, once you explode one, a new one will quickly appear.

• The arena has a bowl shaped wall around it you can jump on or slide down. Enemies can go through this, bombs and the player cannot.

I have a longer more comprehensive guide if you want more information.