Oh, by the way rsync is really powerful and this only scratches the surface of what rsync can do. But you don't need more info to do local back ups.
Syntax:
rsync -options /source /destination
Compare two folders
This command uses the "-v" and "-n" option to do nothing. Instead rsync prints out what would have been copied from a source folder to a destination folder. To delete files from the destination folder see notes on "--delete" below.
rsync -rvn /source /destination
-r, --recursive recurse into directories
-v, --verbose increase verbosity
-n, --dry-run perform a trial run with no changes made
Back up one folder to another
This is all you need to back up a source directory to a destination directory. If unsure try it out with the "-n" dry run option first. To delete files from the destination folder see notes on "--delete" below.
rsync -av /source /destination
-a, --archive archive mode; equals -rlptgoD (no -H,-A,-X)
-r, --recursive recurse into directories
-l, --links copy symlinks as symlinks
-p, --perms preserve permissions
-t, --times preserve modification times
-g, --group preserve group
-o, --owner preserve owner (super-user only)
-D same as --devices --specials
--devices preserve device files (super-user only)
--specials preserve special files
Additional tips n tricks
Test with the "dry run" -n option first to see what files would be deleted and copied.
-n, --dry-run perform a trial run with no changes made
Delete files in the destination folder that does not exist in the source folder.
--delete delete extraneous files from dest dirs
Exclude files that you don't need for instance system files.
--exclude=PATTERN exclude files matching PATTERN
example: --exclude '.DS_Store'
Compress files during transfer to save bandwidth
-z, --compress compress file data during the transfer
Credits
rsync - man page
lifehacker.com - Geek to Live: Mirror files across systems with rsync
techgage.com - Backing Up Your Linux