My "simple" website providing basic Transparency Compliance for a Parish Council (or other small organisation) does not need or feature the ability for visitors to "join" as "members". Apart from the Data Protection implications of capturing personal information there is no need for my Parish Council solution. I can see that there are those that do require this feature.
It is my experience that having a Member Login on a simple Parish Council website that the casual visitor is confused into thinking that you need to sign up to view the contents of the website. Often the Log In button or menu option features promenantly on all pages of the website, this is due to "one size fits all" website design.
The requirement for a Database based website
To implement this effectively there is no real alternative other than to use a CMS such as WordPress or Drupal. You will need to be able to store and catalog the names, IDs and other information on your membership. This can be done in a database, such as MySQL, where the information will be stored in a table or set of tables. In addition you will also need to provide a means for this information to be accessed. A member needs to be given a means to register and to login using their profile.
You could attempt to program a MySQL database yourself, this will probably be offered free with your hosting packing but this is mainly to facilitate the use of Wordpress or Drupal. These CMS use the database tables to store all of you website content. This includes formating data as well as the content of the website. The look and feel of the website can be changed radically by the application of a "Theme" that accesses the core data of the website. The Theme control instructions, most probably written in php, are also stored in the same database.
Member credentials need to be protected and have implications for Data Protection legislation. Members will login using passwords and you, the webmaster, will have to be able to administer your members access rights (permissions) on your site.