From your course homepage select Content from the navbar

From the content area, click on the module or sub-module where the link will be added. In this example we will be using the module titled Unit 1: Poetry

Click on the blue upload/create button and from the dropdown, select the Create a Link option

From within the New Link dialog box, enter a title for the link in the Title field.

Enter or paste the web address in the URL field.

Select the Open as an External Resource checkbox if you want the link to open in a new tab or window.

Click the blue Create button once done entering the required field.

You have successfully added an external link in a module and will see if when the page refreshes with your saved work.