Although you are invited to sign up, you do not need an account if you just want to use the app.
If you want to download your data or create blog entries, then you should register as a member on this site. Membership is free, but please regard any posts you upload here as temporary. Registration is free and can be done at the register page.
If you want to keep your posts indefinitely, upload more then four audio notes, and publish a Podcast, then you should create a WordPress site of your own and install the Psygraph plugin.