basic user name and password

I’m trying to activate the Akismet plugin, but I can’t get the necessary API key without logging into the wordpress.com account. It doesn’t recognize my user name or even my email address, although I logged into it to get to my Profile and Dashboard. I have a user name and password for this forum and different ones for my blog. Do I still need another user name and password for a different account? If so, I don’t know where to go to set it up. Please clarify this for me, and point me to the right source where I can complete this operation. Thanks.