ow to control access to your site. This mechanism should prove sufficient for most people but it is necessary to understand the way this model works.
Basically there are two distinct access control models for websites.
How to give users a way to ask a Site owner to give them access to their Site is not immediately obvious. One option is to provide a link to a part of the site that is only accessible to the Site owner. For example, for the Site philridoutdemosite I could use http://sites.google.com/site/philridoutdemosite/system/app/pages/admin .
This works adequately for 'consumer' Sites but does not work for Google Apps Sites (I know of no way to request access to a Google Apps based Site) and this is the simplest option for most people.
On receipt of a request for access, the easiest option is simply to click the 'allow access' link. But see also how to Control Access with Groups.
An option that will work for any type of Site is to create and embed a Google Form. This has the advantage that you can at the same time ask for any additional information you would like to have from your Site users. It has the disadvantage that adding users as members of the Site will have to be done manually unless you write a Google Apps Script to process form responses and add users to your Site. Again, I recommend reviewing how to Control Access with Groups.
Whether or not you use a Google Group to manage Site membership, you may wish to generate a list of Site members which can be done using this script: Listing members of a Google Site