Look in your quake/fortress/ folder for a folder called QWMCYCLE (may be lowercase). In there you should see files like map0.cfg map1.cfg etc. This constitutes the server's map cycle. If not, or if you're still confused, here's a rip from the TF docs:
Create a directory under the quake\fortress directory called "qwmcycle".
In this directory you can put cfg files that the patch will use.
The directory, qwmcycle, can be overridden by setting the "cycledir"
or "cd" localinfo keys to an alternative directory.
e.g
"localinfo cycledir server1"
"localinfo cd server1" // Abbreviation
Both make the server take it's map cfg files from the
fortress\server1 directory.
Each cfg file should be called "mapX.cfg", where X is the map number in
the map loop.
E.g. If you wanted to cycle between three maps (2fort_32, storm1, well6), you
would make 3 cfg files as follows:
map1.cfg which contains the following line:
map 2fort_32
map2.cfg which contains the following line:
map storm1
map3.cfg which contains the following line:
map well6
NOTE! At the end of the list, you _MUST_ create another cfg file,
which consists of one line which sets serverinfo n 0.
E.g. in the above example, you would also need this:
map4.cfg which contains the following line:
serverinfo n 0
And last, you must put a map command in your server.cfg file which
changes map to the first map in the list, and a serverinfo n 1 to prevent
the first map playing twice
E.g. in the above example, at the end of your server.cfg you would put:
map 2fort_32
serverinfo n 1
There is no limit to the number of maps you can cycle between. You can also
use the cfg file to change any server details. Lets say that in the above
example, you wanted to only allow 16 players onto storm1, and 32 onto the rest.
You would change the following files:
map2.cfg would become:
maxclients 16
map storm1
map3.cfg would become:
maxclients 32
map well6
If you want to make a server rerun the same level over and over again,
you will still have to make a map1.cfg that contains a map command, and
a map2.cfg that sets serverinfo n 0.
N.B. Make sure all the maps in the list are spelt correctly and that they
are in your server's map directory. If they're not, the server will
crash when it tries to enter the map.
N.B. The "n" serverinfo key stores the current map number in the list. If
you want to jump around the levels, you can just set the key to
(desired level number - 1).
e.g. if you wanted to jump to map 3 in the list, enter this:
serverinfo n 2
and then end the level.