I could answer this for you:
You go through the token purchase options, and you select the amount of tokens you want to buy with the web-processor 'Epoch'. You should -not- check the Credit-card box, but rather - the 'Ukash' one. You enter your pin-number and full voucher amount (not the cost of the tokens!) and it also requires a post-code and a name (if you're using a pseudonym, be consistent with it too. I was locked out of my account for using too many inconsistent ones.)
The email address is to simply receive the e-receipt in addition to any remaining money left on your Ukash vouchers. I really wouldn't recommend using it for long though, simply because they may decide to not let the vouchers process when combining/splitting them (which has been a recurring problem for me).
It does say that it only allows credit-cards on the front page, but it accepts the vouchers as well. I hope this helps!