I don't know C# but you should first find a 'tutorial' type thing to get you through the basics. Some people swear by programming books (look on torrent sites if this sounds like your kind of thing) but I never did this. There are free online tutorials, which sufficed me for Python and C (and now Go). Do a search and find a detailed one which you can understand. I found this from Microsoft and it looks okay (maybe a little out of date?): https://docs.microsoft.com/en-us/dotnet/csharp/
A quick look-around tells me that the .NET standard libraries provide a lot of things. You will also want to find a good reference guide to these libraries (e.g. handling files and input and output) to consult when you get stuck in your projects.
If you have the time, I would suggest not starting with C# though. Again, I don't know the language, but I think that something like Python (though it has flaws) is better for a beginner. It's what I first learnt. It's simple to start and can be used in different paradigms (i.e. you can choose to use classes and objects - like C# seems to do - or not). Thus it can be more instructive, while being a springboard for learning different types of other programming languages.
I hope this is useful and not too restrictively specific.