making a TF2 server.

Can any1 please help on how to make internet TF2 server so my buddies can join over the internet. Ive follwed several tuts but no luck. This is what i have done:

Ive downloaded HLDS, installed it at location 'C:\HLserver'.
I created a .bat file and updated the files.
I created a file 'server.cfg' and put it here 'c:\hlserver....tf\cfg

At this point, this is where i get stuck. I know you have to port forward some ports but i dont know which ones and how. I know how to connect to ma router (linksys) but after that i get lost. Like i said iv follwed severl guides but they all confusing.

The server runs fine its just that everytime my friends try to join it says that its not responding. I serch for it on the internet list and it deosnt show up.My friends search for it and it still deosnt show up. Any help would be greatly appriciated...