If you want to display your ads on multiple websites about one particular subject, topic targeting will help you. The instructions below will show you how to add a list of topics to your ad group.
How to add topics:
1. Sign in to your Ads account.
2. Select Display Campaigns from the navigation panel.
3. Choose Topics from the page menu.
4. Click the pencil icon.
5. Select an ad group.
6. Choose an ad group to add topics to.
7. Select either Targeting (recommended) or Observation.
8. Optional: In the table, choose specific topics to narrow your targeting.
9. Click Save.