You should opt for CSE branch in engineering it will give you a foundation in this field.

The major platforms are Android, Apple and Windows. You can learn to code for all of these platforms, but you probably need to choose one when you're first staring out. Android is the dominate market, but Apple is not far behind. One of these two would be a good place to start.

You should also develp marketing skills if you want you can also opt for any course related to it.

Good Luck!!

Along with that, you should be good with programming language like  C, C++ and Java etc as this is the main requirement for the same.

Good Luck!!!