Okay, some instructions to get you going - I’ve literally just tapped these instructions out but I’ve tried both possible options on the default content and they work okay

You basically have two options and I’ve explained below what you need to do for each of them. I’ll leave it up to you which one you choose to roll with.
Note: The downside to the Personalize route is that because of the way it will be setup (having nested snippet calls), you will need have all your pages as
uncached. Otherwise, the parser won’t render the WebLogin snippet correctly.
Route 1: Using Web Users and Document Groups
Setting up the User Group and Document Group
1. Go to Security->Web Permissions from the top menu when logged into the MODx Manager.
2. On the page that loads, under the ’Create a new user group’, add a new user group with a name of your choice.
3. Now select the ’Document Group’ tab.
3. Under the ’Create a new document group’, add a document group with a name of your choice.
4. Now we need to link the user group to the document group so select the ’User/Document group links’ tab.
5. You should the Web User Group listed that you added in step 2 above.
6. From the dropdown in the Document Group column, select the Document Group you added in step 3. Click ’Add’.
To restrict page access to only people who are assigned to the user group you have just added - all you have to do is select the Document Group from the list of groups under the ’Access Permissions’ heading when creating or editing a document. (The Access Permissions are at the bottom of the document editing screen, under where you edit the document content).
To add a web user to the user group, log into the Manager and go to Security->Web Users. Select the user in question and on the edit screen you can scroll to the bottom of the page and select the user group from the ’Web Access Permissions’ section.
Route 2: Using Personalize
Setting up the Personalize snippet and the required chunks
1. In the MODx Manager, go to Manage Resources and select the Snippets tab. Do you see Personalize listed? (this depends if you installed the default content or not). If you don’t, click the ’New Snippet’ link and paste the contents of the Personalize file you have into the Snippet Code textarea. Call it ’Personalize’ and hit the save button.
2. Now select the ’Chunks’ tab from the Manage Resources page.
3. Click the ’New Chunk’ button and on the chunk editing screen give it name of ’loggedIn’. In the chunk content, type the following (we’ll keep the content really simple at the moment):
4. Save this chunk.
5. Create another chunk, this time calling it ’notLoggedIn’ and for the chunk content use the following (if you are using WebLogin with a different form template, then adjust the following snippet call accordingly - if you don’t have the WebLogin snippet at all then you’re best retrieving it from a MODx install that has the default content):
[!WebLogin? &tpl=`FormLogin` &loginhomeid=`[(site_start)]`!]
6. Save the chunk.
Adding the Personalize Snippet to the Template
1. Go to the template editing screen in the Manager for your chosen template.
2. Add the following code where you would normally place the main page content:
[[Personalize? &yesChunk=`loggedIn` &noChunk=`notLoggedIn`]]
3. Save the template.
Now, as long as you use that template for your pages (you can obviously add the snippet call to any other templates you may have) - if the user is logged in, they will see the main document content. If the user is not logged in, they will see the login form.
Tweak to your heart’s content
Hope that helps,
Garry