An invitation is sent to you via email by Catenda with a link to the next steps of registration. Using this link you can create an account with your personal credentials.
After your registration is complete, you can access your projects on Catenda Hub from any web browser.
https://hub.catenda.com/signin
Further reading: Sign in page, Creating an account, Landing page
Find step 2 in getting started on the help center or in the help menu.