When you are using the Manage Backup Sets Wizard, you can choose to exclude files from your backup set.
If you want to backup the majority of a folder or drive and exclude only portions of the folder or drive, it is best to select the entire folder or drive to INCLUDE in the backup set. Then, at the Exclude panel, select the few items that you do not want to include. When you use this method of including everything, excluding a few specific items, any new items that are added in the future are included in the backup by default.
The goal of the exclude panel is to remove specific items from a backup set. It is always best to "over-include" more data in the backup set than to accidentally "over-exclude" data that may be needed in the future.