I need to know how to load a map on a server.
Open you console with the ` key.
Type /callvote map <mapname>.
For example to get Poseidon B you would type /callvote map rpg_poseidon_b
(note that if there are others on the server, they all have to vote for the map as well by pressing F1 - F2 votes no)
You can find the map name by opening the map's .pk3 file and finding the map name within the maps folder.
You can open the pk3 by downloading its registry key from effiles (which I highly recommend) or by TEMPORARILY changing the file extension from .pk3 to .zip. (be sure to change it back to .pk3 afterwards)