I have a steam key but how do I use it?

Any help is greatly appriciated

let me clarify my friend has a steam key but niether of us know how to use it.

Please see here: https://support.steampowered.com/kb_article.php?ref=5414-tfbn-1352

I’m sorry Jan I went to that link and all I got was

Error 503 Service Unavailable

Service Unavailable

Guru Meditation:

XID: 1736135510

Varnish cache server

Please continue to help

I get this:

Maybe a temporary issue at their site?

got it working thanks again Jan