DESIGN : small map application with database

I would like to create quite small web project:

Even single web application with map (can be google map) displayed. User would have the functionality to pick some points and then the coordinates would be saved in database. Also he would be able to see the points on the map provided by other users.

In future : maybe later would be nice to create mobile application with the same functionality and with common database. It's important that web app and mobile app would connect to the same DB.

How to start? What is the easiest and fastest way?

I am familiar with html, java ee, jboss, postresql. I created the account on openshift and maybe it's good place to create database? I am also wondering will I need to run server or just some web hosting will be enough.