I want to develop shopping app for android and it should works like tinypay.me

Users can sign up and they sell items or buy items immediately.

I need to database. I want to use SQLite but I don't find any answer to these questions:

• SQLite database files are stored on the user's phone, isn't it ?

If it's true, here is the scenario:

User logged in, then he/she wants to sells something on app. He/she creates ad and he/she published it on the app. These variables writing their database.

When other users logged in, will they see this ad? If it's possible, how can sync database between users ?

Thanks for attention.