Router settings are so confusing please.. help mee

Well, i have had a few threads so far asking for help because i really want to play Left 4 Dead with my friends online.. sadly, my router will let me do nothing of the sort. Anyone who has a router from SMC should know how to do this. This is my router-
http://www.smc.com/index.cfm?event=viewProduct&localeCode=EN_USA&cid=1&scid=17&pid=924
One of the instructions i found was to go to the settings and edit the special applications and enter the numbers at the bottom of this page-
https://support.steampowered.com/kb_article.php?ref=6776-MYXU-0480
Now.. how should i do this? It has something to do with a trigger port and public port but i have no idea how i am supposed to plug in these numbers! Pleaasee, i beg for help! Ty

 

wow that site is a god send.. thanks a bundle! Now for the static ip, would i have to contact my service provider for that or something? And would it influence all the computers on my network? TY so much

 

haha, nevermind, found it! THANKYOU Digitalocksmith!!