It's pretty easy, sign up using the link at the top right.
We recommend authenticating with your flickr on a read-only basis, though it's not essential it helps us make sure it's you, we're only displaying your specified public content. All of which links back to flickr as per our agreement with flickr.
Once you've signed up, you get your own username.portfolir.com which anyone can visit, so good for your blog, or your business card, or for tagging down at the local bus shelter (not that we approve of graffiti of course)
Then you select a set from your list of flickr sets, and you're good to go. (We're adding Portfolirs by tags and of your phototream soon).