Enter the Twitter account name and click on the Create Widget button
Copy the generated code to your clipboard
On your course page add a new HTML block (you add a block at the bottom of the left column of the course screen)
Configure the HTML block to add the content. First expand the editing toolbar using the Toggle toolbar button and select the HTML editor button which on our Moodle is shown as <> (see screenshot below)
Paste the code (from your clipboard) into the Content area, then click on the Update button.
Give the block a title (eg. Twitter Feed) then click on Save Changes.