This is a pretty loaded and broad question, but luckily, there are services that are built to get you up and running with minimal friction. One of my favorites is StackMob. You can easily create a remote database, and use their Android SDK to sync with it. They also have amazingly simple connection to Amazon S3, to easily allow file uploads.
The best part: It's free for basic usage. They've taken an à la carte approach, that allows you to create a full web service, with only the add-ons you need. To simply have a remote database and S3 connection is free.
Start here: https://developer.stackmob.com/start