Please complete the following steps:
- Setup your Google Adsense account.
- Make sure that your WordPress theme contains necessary hooks for ads displaying (the_content, wp_footer, etc). If you don't know how to check that, just install any official WordPress theme (for example, Twenty Twenty) and check if the ads are displayed. If yes, it means that the necessary hooks are missing in your theme.
- Make sure Adblock (or similar browser extensions) is disabled in your browser.