You will need to follow some more steps before you do this:
1. Download MW2 Liberation v1.04
(for donor-functions take a look at YouTube: MW2 Liberation v1.04 Donor-Unlock
2. Download LobbyTracker
3. (optional) Download some mods to host (Search on MPCForum
4. Create an account on http://www.itshax.com/LobbyTracker/register.php
5. Run LobbyTracker and login there. It should say "Waiting..."
6. Run Call of Duty: Modern Warfare 2 with MW2 Liberation
7. LobbyTracker *should* say "Ready". Don't close the program now because it stops keeping your lobby on the list as soon as you close it.
Actually this also works without MW2 Liberation, but since hosting games with Mods (not joining!) is VAC2 detected and most people come here for this being modded games it's highly recommended to use a tool like MW2 Liberation to disable VAC2.