How do I put the users steam account into a variable?

I want to make a horror game that takes place on a windows 7 desktop. I am a huge fan of meta game play and I think it has huge potential for horror. With inspirations such as IMSCARED and Doki Doki literature club (spoilers, yes it is a horror game) creating files on your computer and pulling this trick, I decided to make a meta horror game. How would I take the users steam account name or their computer’s name and put it into a variable, so I can call them out by name.

here is the example from ddlc: Let's Players Reaction To Monika Knowing Their (Real/Steam) Name | Doki Doki Literature Club - YouTube

To do that, you need more knowledge on c#. Your question is proof enough that even if i explained what to use, you wouldn’t know how. I suggest you go do some tutorials on c# before trying to do this. But it is definitely possible.