Select difficulty, and enter your nickname.
Use the analog stick to move the character.
Tap on the screen to shoot.
Tap the Big button to sprint.
Tap the smaller button to reload.
Tap the floppy disk icon to save.
The yellow text on the right is your ammo.
The % text is your HP.
Keep an eye on your ammo and what time it is. Zombies become more aggressive the later it is.