In Europe, after filling that membership form online you will be sent to paypal. I tell you this so that you don't become surprised; there you will pay for your membership, so you need a paypal account or a credit card I believe. I don't know if there's another way.
It may also be good to write an e-mail to the Gar you'll be affiliated with and ask for your login data and DC card number.
They may advise you to ask for your login data (to see the replays of the webcasts) to the webcast crew.
It's also cool to subscribe norbunet mailing list to keep up to date with events.
If you are a new member, be sure to read the advantages offered, like being able to discount the price of your membership in the first retreat that year and so on. If you have financial possibilities, consider not doing this though (my personal opinion!), since the DC needs funds to realize its many merit worthy projects. But you can, and if this helps, why not?