There can be different reasons why ads are not showing on your site after you've added the AdSense code.
First of all, you should know that Google will not show ads on every page of your site because it pulls out the keywords of your page and then finds what ad matches your content. If there is no any related ad to your content, no ads will be shown.
Another reason is your internet connection. If it's too slow, then the ads will be not loaded or it might take a while for the ads to be loaded. Or maybe their artificial intelligence system couldn't figure out if the ads have a potential to be seen and clicked.
You can access your page(s) from another PC or from your mobile phone to see if there are ads that appear on them. Make sure that you have disabled any ad blocking app and that you cleared your browser cache and deleted your cookies before trying to access your site again.
Make sure that the ad code is correctly implemented in your site. You can do this by viewing the source of your site from a browser and check if the ad code looks exactly like the code Google provided you in your account.
Another reason why Google Adsense Ads may not be showing up on your page(s) is when there is not enough content on your site or there are too many ads per page.