Some C# and .NET resources that I think are great.
- Microsoft Docs. I recommend starting here, there are a lot of great guides and information there
- Pro C#. A great book for learning more C#. It is a little bit dated, because of the focus on .NET Framework but all the stuff about the C# language is still relevant
- This Microsoft book about Design Patterns are great, and I recommend all C# developers to read it, and re-reading at least once a year. I learn something new every time I read it.