On the tab "General" you can decide what file endings are supposed to be included in your backup. If you click on the button 'Edit' a new dialog will open, with which you can easily include files or exclude files.

Use drag&drop in order to add files to the backup.
You also have the option to exclude files from the backup. Just choos a directory or a file and drag&drop it in the 'Exclude files/directories' window.
Of course, you can also use the 'Add file' or 'Add directory' button.
