You will find all available commands including explanations in ProCon itself. To do so, simply click the desired plugin and check the "Details" tab.

The basis commands are outlined here.
Requires the plugin "In-Game Admin" to be active and a player account to be set up!

@kick player name Kicks a player from the server.

@ban Bans a player from the server. 

@kill player name Kills a player.

@say text Sends a message to the server.

@restart Restarts the current map.

@nextlevel Changes to the next map in the map cycle. 

@move player name Moves a player to the other team.