Try putting this into the console
"sv_lan 0"
"IP yourexternaliphere"
Then have people connect using
"connect yourexternaliphere"
nonononono
If you can, try finding an auto config in your router that sets it up as CS:S or any other Source multiplay game.
After that you have to do 4 things
"sv_lan 0; sv_pure 1 (2 if you do not want skins); ip <external IP excudeing ports>"
changelevel "mapnamehere"
Read the console to see if your server is secure in VAC
Invite friends and stuff your self at the fact that there are no decent admin mods.