When to use the Sync method versus the normal method and when to use await

[velara3]

I have a class that I am using with this project and sometimes it has errors or returns an string that says, "Did you mean to use the sync method?"

When do I use the sync method and when do I use the non sync?

Also, I use await in my project. Do I have to do the same?

When do I know when to use the await method?