Enable anonymous users and then create the pages you need. https://docs.mendix.com/refguide/anonymous-users
Be careful though: it can be tricky from a security point of view
I hope this helps.
In a microflow under the save button pass the registration entity and create Account entity with the values. Make sure your password validation matches and usernames need to be unique so also cover that one or else your commit with fail.
Make sure your registration entity is non persistent or deleted, so you don't end up with unhashed passwords in your database.