First thing you do is restore the FULL backup, and then you restore the latest DIFF backup. That's it! This is assuming no FULL backups were taken in between the DIFF and the FULL you are restoring from (only exception is if you used a COPY_ONLY option in your full backup but most likely that wasn't the case). Remember to use WITH NORECOVERY on the full restore so you could continue to restore the DIFF.
In the rare exception that the DIFF throws an error stating that the LSN's don't match and your full backup is not the right one, you can query MSDB or right click on the DB, go to 'reports', and 'backup/restore' history. That'll tell if a full backup was taken in between but by the sounds of it that is not the case. On the DIFF restore make sure to state WITH RECOVERY to replay the log.