Hi Oberdan:
I suggest you explore the various Wix tutorials, articles and examples and get familiar with the platform.
For example you can perform input validation and display error messages in a variety of ways. Custome validation is one way andit is explained at this link.
https://support.wix.com/en/wix-code/user-input
Adding additional forms for password entry and validation check these links:
CReating a new member record and adding the user information into a local data collection check this link out:
Cheers