How to promote app with Adwords CPI??

So I’m thinking of having an app made, but I want to promote it using adwords CPI basis.

How can I let adwords know if someone installed the app so this CPI system can work?

How do they track installs? Anyone have experience running CPI campaigns on adwords for their app?

I dont try this, but i learn that it good to try in little budget and see resulats.

anyone? do we need put some SDK or how does adwords know if there was an install?