Developing App,User must be able to add marker on map help!

I want to create application which must do something like this: when someone starts application it must locate his location, okay thats not a problem but what I want to do is this.

I want to put markers on map (customized) and when user starts apps markers must be updated in app, I mean if I will edit it in web it must be displayed on app too, and user must have function to add "marker himself".

I'm creating live traffic application and I want to user add on map if there is traffic jam so there is question: what I will need, how can I do that with google map, just tell what I'll need for that?