The web modules consist of the tools you need to add and edit your site's pages and the content on those pages. I would ignore what the "About Modules" say about these modules. This description is generic and in some cases misleading.
Provides the content for the page currently highlighted in the page tree in a columnar format according to what column the content is in. You can also edit the page properties from here.
List is the work horse of Typo3's web modules. You can add, edit, delete both content and subpages from list. You can edit page properties and move content and pages from list. You can change back something you didn't mean to change and find out where the content and/or subpages are being used in other pages. You can create and manage new versions of pages or content. You really can do anything you need to from List.
You can find out quite a lot of information about any one single page from this module. This module is different from the info found in the list module. From here you can find out basic information not only about the page you are currently on, but up to 3 levels of subpages. Log can show you who edited the page last.
Access will show you who owns this page (and any subpages up to 10 levels) and what group it belongs to. Do not change any of these setting or your editors may not be able to edit it.
Functions allow you to add up to 10 new pages at a time or sort your page according to pagetitle (the page name, not navigation title), subtitle, creation date/time and last changed date/time. You can also reverse sort them.