Logging in.
Go to http://mydomain.tld/manager (replace mydomain with your domain name).

Enter your Admin Username and Password and push the Login button.
Editing your pages.
The Basics.
In MODx webpages are called Resources.
After you login you will see your site tree appear on the left hand side of your window. In that tree you will the web pages of your site and the structure in which they have been organized.
Each resource has an ID : a unique number to identify it.
Next to each page name there is a number between brackets, that is the page's ID (a unique number to identify each resource).
Let's say that in your site tree you see this : 
Then your home page has the ID of 1, your about page ID is 2 and your Contact page ID is 4.
Resources can have different states of accessibility by your visitors.
A Resource can have several states it can be : published or unpublished, hidden from the menus or visible in menus, and finally if you are editing a page then it will appear in bold.
Let's say that in your site tree you see this : 
This tells you that your homepage is published and visible in menus, your about page is unpublished but would be visible in menus if it where published, your blog is published but does not appear in menus and the contact page is unpublished but would not appear in menus if you where to publish it.
To edit a resource : open it, make changes, click save.
If you click on a Ressource it will open it for editing : a form with many fields will appear. You can make the requested changes in the form fields and then click "Save" and the changes be effective. To view the changes on the page - as one of your site visitors would click on "View".
The Main Resource Fields and What They're for.
Here is the typical use of these fields in the websites I design (seen as MODx is so flexible the use of each of these fields depends on the choices made by he who built your template).
Title : the short and catchy title of you page (that is visible in the content)
Long title : a longer version of the title that will appear at the top of visitor's browser window, this is an important place to put relevant keywords.
Description : an accurate description of your webpage (important for search engines).
Summary : a summary of what you talk about on your page/post, I usually only use this field if the page is a blog post.
Parent Resource : the ID of the page's parent : in other words the ID of the resource that contains this page.
For example let's say you have a blog about cooking and psychology. These two categories will be child resources of the main Blog resource and they will appear in your site tree like this :

A visitor will be able to visit http://youdomain.tld/blog/psychology/ for posts on psychology or http://youdomain.tld/blog/cooking/ for posts about cooking.
So if you are writing a post about cooking you want to make sure that the id of the parent resource is the one for your cooking category, in our example it would be 5.
Menu Title : this is the name you want to give your page in your site's menus (navigation), it enables you to use something short to save space or to make it more user friendly (you might want to change the typical "Contact" to "Get in touch" or "Drop me a line".
Resource Content : this is the main content of your page, typically a mix of text and embedded media such as images.
That's it for the main fields that are (almost) always used. It happens that there are additional fields for specific purposes (adding tags to blog posts for example) in which case I make it quite clear what they are for.
The languages field (template variable) in multilingual sites.
If your site is multilingual then you will probably find a field (might be in the Template Variables tab) called languages, this is used to specify the IDs of this page in different languages like so :
en=10,fr=23,es=44
This tells MODx that the resource with the ID of 10 in English is the equivalent of the resource in French with the ID if 23 and the resource in Spanish with the ID of 44. Generally speaking the site(s) will function without you filling in this field but you will have to fill it out in order to display flags with links to the same page in different languages.
Adding internal links to other pages of your site.
Here is a useful thing to know about adding links to the other pages of your site in the content. You can get MODx to generate the URL of your pages automatically.
In Revolution, the tag to get MODx to generate the url for you is this : [[~id]] where id is the ID of the page you wish to link to. So to add a link your html would look like this :
<a title="Link title" href="[[~id]]">link text</a>.
In Evolution it's slightly different : [~id~] gives you the url, so the html would be :
<a title="Link title" href="[~id~]">link text</a>.
This is very useful because if you where to move your page or change it's alias, the link would not get broken.
Managing user comments and newsletters.
If your website allows visitors to post comments or signup to a newsletter then you will have to moderate the comments, keep track of your newsletter subscribers and send newsletters. Depending on the branch of MODx that was used to create your website there will be different ways of going about this.
In Modx Revolution.
Comments with Quip.
In revolution, I usually use Quip for allowing user comments (this blog uses Quip for comments) To moderate (publish / unpublish / edit / delete) the comments you have to go to the "Components" menu and then chose Quip. The rest is fairly straight forward.
Newsletter with Ditsnews.
For newsletters in revolution I use the ditsnews component. Likewise you will find the interface for managing subscribers, groups and newsletters in the "Components" menu in the manager. Please note that creating a new newsletter involves creating a new resource and specifying that resource's ID when you're ready to send it.
In Modx Evolution.
Comments with Jot.
Jot comments are managed directly on the pages where they get posted, just log in to the manager and then visit the page and you'll see that little "edit, delete, unpublish" buttons have appeared next to each comment. Twiwiwytii uses comments with jot.
Newsletter with EasyNewsletter.
In the modx evolution manager, you will be able to follow subscriptions and send emails with EasyNewsletter in the Modules tab.
Logging out.
To log out click on the logout button at the top left of your manager window.

This should be enough to get you started updating/managing the content of a fairly simple website + blog. If you have any questions, or feel like I have missed something that is essential to getting started, please drop me a line or leave a comment.
Comments (1)
Robin Darlington:
Sep 12, 2011 at 02:30 PM
I just realized that comments where not working (perhaps after a revo update) and I have fixed them. So feel free to start commenting - now that it is possible.