This is probably more of a general developer like question

Anyway before moving on and creating large applications, make some simple applications like a calculator or a simple text editor. As for understanding code read some tutorials.

Have a look at this site
http://www.functionx.com/csharp/index.htm

Anyway maybe look at examples and try figure things out. Like:

A <- 6
B <- 6
FOR COUNT 1 to 3
A <- A - COUNT
B <- B +A
OUTPUT A,B

That is an example of code in a NS-Diagram that my teacher gives the class often. No IDE to work it out has to be done on paper. Once you get the handle of that it is easy

Output is A = 0 and B = 14