What applications shall I make to build on my skills(C#)?

Quote:

So I am kind of new to programming and I wanted to build on my programming skills. I just don't to what to build that will stretch my knowledge.

You will not learn programming by making apps, you will learn by studying programming techniques. Making apps are exercises to practice on the lessons.

My guess is that you are learning programming.
You have to know that you can do pretty much anything in any language, simply some languages are harder for beginners because there is more pitfalls to handle.
You need to master a set of techniques that are the basis of the job and are not linked to a language.

Advices:
- Start with an easy/safe language: VB, Java, C#, not C or C++
- Read documentation / Follow tutorials (a lot of them)
- Start with tiny/useless projects, the purpose is to learn programming, not doing something useful.
- Start with console mode programs (no fancy graphics, no mouse)
- Learn debugger
Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Debugger - Wikipedia, the free encyclopedia[^]
- A problem ? Google is your friend.
- Learn Boole algebra
- Learn one or more analyze methods, E.W. Djikstra top-Down method is a good start.
https://en.wikipedia.org/wiki/Top-down_and_bottom-up_design[^]
https://en.wikipedia.org/wiki/Structured_programming[^]
https://en.wikipedia.org/wiki/Edsger_W._Dijkstra[^]
https://www.cs.utexas.edu/users/EWD/ewd03xx/EWD316.PDF[^]
- Learn SQL
- Learn Databases design and Administration
Introduction to database design[^]
1NF, 2NF, 3NF and BCNF in Database Normalization | DBMS Tutorial | Studytonight[^]
- Learn Regular Expressions

Interesting link:
Learn to Program[^]

There is no shortcut to knowledge, no one can learn for you, you are the only one that can do it.
Remember the exercises and little projects are not here to make something useful, they are here to teach you programming.