a) Cut/copy and paste allows you to select a section of text and insert a new copy of that text. You can also transfer data from one place to another.
b) Save is when you keep your work for later and it will be the same as you left it. Think of it like putting a bookmark in your book. Save as lets you name the files.
c) Close and Exit just let you leave the program, saying you are finished working with it and want to do something else.