Joomla modules are designed to work in module positions. However, many users requested to have the ability to use Joomla modules inside Joomla articles. For this purpose, Joomla comes with functionality to display module in content.
First of all, your module should be published in available module position. Usually, if you publish it in a module position, in example 'user1', it will be shown in the place reserved for that module position. And you don't want that. You want the Joomla module to be shown in the content area only!
To achieve that, you would probably need to make an additional module position in your template. It can be done very easily. Open file "/templates/your_template/templateDetails.xml" in a plain text editor (such as Notepad). You will see all module positions listed between <positions> and </positions>. Add one more module position by adding this line, for example:
<position>myposition</position>
Make sure that position name is unique. The new module position that you have just created would be available in the list of module positions (when you edit any Joomla module). Now, you have a module position that's available for use in Joomla, but not implemented anywhere in the template code. When you publish a module in such a module position, it won't be shown anywhere on the site. This will allow you to insert it only in the content area of your Joomla article.
The code snippet is for Joomla 1.5 and above. Enter this code anywhere in your Joomla article where you want to show the module:
{*loadposition myposition}
Remove the asterisk (*) from this code. We have added it to prevent the loading of the module on this page. Also, change "mypostion" with the name that you gave to your module position.
Now, there's an easier method available!
During 2021, we released the Sparky - Joomla Page Builder. Besides many other features, it also allows you to include modules in the articles. This article from the Sparky Page Builder documentation explains how to do that.