It's important to understand the difference between enquiries and members. A member exists permanently, and should only register once. Where as an enquiry form, survey form or custom form might be submitted multiple times during the life time of a customer.
You can use standard enquiry forms, custom forms, survey forms etc. These will all appear as messages/enquiries under the "Enquiries" tab in the CMS. It is expected that a customer may interact with these forms multiple times.
If the email address is known to the system, the enquiry will be associated with the existing member.
If the email address is new, our system will create a new member record using as much information from the enquiry as it can.
We have purpose built "member registration forms" and these are tied specifically to the members list.
These forms can be customised, but have a more rigid design than enquiry forms.
The member record may already exist in the system, and there are some choices you can make as to how new submissions are handled, as to if the new data overrides old data, or not.
Remember that member records can be created by several means, not just forms or member registrations, but also online shopping, forums, and contact form enquries. This is done specifically so that there is only 1 member record to ensure that all a members activities can be tied together.