Access the Scanner through Menu -> Preferences -> Scanner
Setting up the scanner is fairly straightforward. You first want to add the location(s) of your music. Press the Edit Scan Paths to bring up the popup in the image above. By default /mnt/sdcard and /mnt/sdcard/Music will be added to the list of paths/folders. To remove a path from the list, simply click the list item and press the remove button. To add a new path you can either type it in manually in the edit box, or press the browse storage button to bring up a list of paths found on the device. Once selected press the add button to add it to the list. Click save to save all the changes.
Once the scan paths are setup, you can add specific paths to ignore the same way. Press the 'Edit Ignore Paths' to tell the scanner what paths to skip over.
Delete database before scan: Wipes the entire database before running a scan. This option is not typically needed but is present in case the user wants to start fresh without having to uninstall then reinstall.
Only scan new files: If this is enabled, any file that was already scanned into the database will be automatically skipped over. If you are using an external tagger to retag your music, disable this option to pick up all the changes.
Ignore folders with .nomedia: This is a behavior that the default android music player follows. Any folder with a file named .nomedia, will get skipped over. This is useful if you have folders with ringtones or other sound bytes that you do not want showing up into GMMP. Note: the ignore paths can also be used to skip these paths.
Format artist/album tags: Artist names and album names will be formatted into proper case before being entered into the database. This is useful if your music collection is not tagged to any standard. Example: I have 3 albums by "insert band name here". The first album the artist is tagged "Insert Band Name Here", 2nd album "INSERT BAND NAME HERE", and 3rd album "insert band name here". With this option off, each album would be recognized as being from a separate artist. With this option on, all 3 albums are inserted into the database as the same artist "Insert Band Name Here". If you have taken the time to properly tag all your music, you will not need to worry about this option.
Ignore AlbumArtist tag: By default the scanner will use the albumartist tag if it exists instead of the artist tag to label albums. Enable this if you want to ignore that tag
Scanner Menu Options (Press the menu button in the scanner)
Clean Database: Removes any missing songs, artists, albums, or genres from the database. This is typically done at the end of a scan, but it can be done independently as through this option.
Setup Auto Scan: This sets the scanner to run at the given interval
Database Stats: Shows the number of songs, artists, album artists, albums, and genres scanned into the database