The Google Adwords global site tag should be placed in the <head> section of all your pages, while the event snippet should be added to the <head>section on the conversion page itself. Copy both code snippets from Google Adwords, then follow the steps below.
Add the global site tag to all your pages
In your HubSpot account, click the settings iconsettings in the main navigation bar.
In the sidebar menu, click Website > Pages.
Scroll to the Site header HTML section and paste the global site tag snippet here. If you installed a global site tag on your website from another Google product (e.g., Google Analytics) or from another AdWords account, follow Google's documentation to adapt the tag so it works for your AdWords account.