Web users cannot edit documents (resources) unless you install some kind of front-end document management, and create form pages for them to enter material and snippets to handle the input.
Web users who belong to the relevant permissions group(s) can access documents (resources) that are assigned to those groups in the Web Permissions tab. Others who visit restricted pages will get a 404.
A standard manager user can edit resources according to a combination of the role assigned to them and membership of a user group with access rights to the relevant resource group. Out of the box, there’s only one role, that of Administrator. You can create new roles, restricting the actions available to a user given a particular role. For instance, you may allow a certain role to view and edit documents, but not to do anything with snippets or chunks. Users’ opportunities are further restricted to specific sets of documents using the user/resource groups links in Manager Permissions.
In MODx 1.0.2, you’ll find the checkboxes to assign resources to resource groups in the Access Permissions tab alongside General and Settings tabs at the top of a document opened for editing.
The first thing is to get the distinction between web users and manager users clear in your mind. Then you can try creating document groups and some simple roles for manager users. If you take it step by step, it will eventually make sense. If you try to take it all in at once, you’ll probably end up v. confused.

KP