This is in no way a task for a beginner - it is a complex job that risks losing all your data if you get it wrong. In addition, trying to do this in any .NET language is fraught with problems - the first being that not all systems (even in the PC world) have the .NET framework. And if that isn't loaded, your C# code can't work...
Instead, consider using something like
TrueCrypt[
^] - it's free and open source software.