rsync is a great swiss army knife for all kinds of uses. as such, it is fairly complex. here are a few neat tricks.

rsync as a server

for security, rsync is typically used over ssh. suppose, however, that you wanted a read-only, publicly accessible repository. kind of like a public ftp site, but with the advantages of rsync.

# apt-get install rsync

edit /etc/rsyncd.conf
[myshare1]
path = /home/me/share1
comment = some stuff
use chroot = yes
read only = yes

[myshare2]
path = /home/me/share2
comment = some more stuff
use chroot = yes
read only = yes

edit /etc/inetd.conf
rsync stream tcp nowait root /usr/bin/rsync rsyncd --daemon

restart inetd:
# /etc/init.d/inetd restart

now, on the client side, you whould grab one of the repositories like so:
client> rsync theserver::myshare1 .

if you wanted to see what was available, leave off everything after ::
client> rsync theserver::
myshare1     some stuff
myshare2     some more stuff

rsync over ssh without password

On both machines:
> apt-get install ssh rsync

To get rsync over ssh working without specifying a password, you need to put an authorized key on the machine you want to connect to.

See ssh keys for more information.