1. Go to the link https://tagmanager.google.com

2. Select your account

3. Click "New tag" and enter its name, for example Looksize.

4. In the "Tag Configuration" section, select "Custom HTML" and insert the Looksize script.

5. In the "Triggering" section, select "All pages" and click Save

6. After you create a new tag, you must submit it to the site. To do this, click the Send button that appeared at the top of the window. 

7. Fill in the Version Name, Description, and click Submit