Yes, you just go to the chat lobby, arrange a match, play it here on WGT.com, then go back to the Ladders site and record the match result there. The match result will move you up or down a ladder, a tournament table, etc.
That's all. If you need more help, just ask.
You might also want to read the Ladders Site Manual and read all the threads in the Announcements section in the ladders forums.