"On your Joomla administrator page"
Go to "Content" menu and click Article Manager
Look for an article you want to have an mjform then click.. for my example i chose "Getting Started"
Now below the form, you will see the Mjform button. Click it
You will see a pop-up window.. Select the kind of form to be inserted
at the end of your form you will notice {mjform=1}. This is the syntax for mjform. You can transfer the mjform wherever you want to place it in the content. Click Save and Close
After Saving you will see a successful message