To aim, just touch the screen and move your finger slowly. This way, you can see the trajectory of your arrow. Keep in mind that the enemies are running in your direction, so you'll have to adjust your shot accordingly. Just one arrow to the head is enough to kill just about any enemy.
As you beat levels and advance in the game, you unlock new bows and types of arrows. In fact, you should use your arrows carefully because they come in limited quantities, so if you run out, you'll have to buy more.
Tiny Archers is a super fun action game that also has a huge number of levels. The best part? You can unlock new characters when you complete all the levels with the original archer. The graphics are also a real treat.