What if your app needs a backend system? What do I mean backend system? Here is a scenario where a mobile app needs to do some backend computations and transactions

Backend systems may include (minimally)

server-side code (you could have any language here) --this is typically a web server-side program (using CGI and HTTP)
database /data solutions (this may be a traditional database like MySQL or Oracle or more elaborate Data Distributed solutions)

You need to know server side programming
You need to understand database/data solutions and how to connect to them via code
NOTE: you can take CS3520 and CS6320 to get these skills

OPTION 1: or this class only (not for a deployed application) I can get you an account on a PhP server and an Oracle server --but, they are shared and there can be issues with down time
OPTION 2: you can go to a hosted solution (pay for it)
OPTION 3: you can go cloud BAAS options(and there are some free tiers --you need to check those out)

If you go with option 2 or 3 you are repsonsible for any setup and fees involved not me.
- Real android app programmers may choose to use the cloud --for example there is a free tier on Google app engine which is Platform as a Service cloud and discussed here https://cloud.google.com/ solutions/mobile/

Relational DBMA tool: If you are using a relational database on the back end like Oracle or MySQL you will need a DBMA(database management administration) tool. There are many.
- TOAD has a freeware version you can read about in module 13 of the following outline http://algebra.sci.csueastbay.edu/~grewe/CS3340/outline.htm
PHP and MySQL backend for Android Tutorial:Here is an arbitrary tutorial on using backend of PHP and MySQL with Android App --- I did a quick search on google you can find your own favorite. http://www.tutorialspoint.com/android/android_php_mysql.htm