Like kcrat said, you have to wait until July to SUBMIT everything. But if you want to look around/check out the format you can create a username and password now and you can look around. But when July comes around the information you entered (if you entered any, although you'll probably just look around) will be purged and you'll have to start all over again (including contact information). Even your username and password will be purged from the system.
I did this for this cycle, albeit on accident (I wanted to get a super head start on the application so I created my account in May then I received an email from PTCAS advising my account is going to be purged and PTCAS won't be available Again until July)