You need an open project, to start a new project go either to File>New>Project, or press Ctrl+Shit+N.
Preferably choose the Empty project template.
Then, right click on the Source Files folder to the left and choose Add>New Item...
Then you get a dialog where you can choose the name of your file. When choosing your name, don't forget the .c extension.
After writing your code you are ready compile. Do this by:
My "green button" is gray for some reasons,
that is to say it looks disabled.
Can't find any button that says build, compile, or run.
F7 doesn't work either,
is there some extras I might need to download before??