Hi

First of all start off with C. C language is very fundamental language. It helps you in building up your basics in algorithm, loops, iteritaion etc.

After C you can learn C ++. C ++ is object oriented programming language, it is much easier than C.

Then learn php and Javascript.

Now to build app there are many softwares ready made software available in market.

The most popular are Andriodstudio and MIT inventor 2. Both this software are free and are easy to use.