How do I make user customize timer?

Hi, GS dudes.
I am gonna make user customize timer. When user want to set timer in app, it must be set what user want and be displayed. It also should have function of stop and pause. (like the basic app in iPhone) How do I make it? Please give me an example.
I am gonna make user customize timer. When user want to set timer in app, it must be set what user want and be displayed. It also should have function of stop and pause. (like the basic app in iPhone) How do I make it? Please give me an example.