There are three ways to put the Message widget on your site. Pick the one that matches your stack.
WordPress, Shopify, Wix, Squarespace, Webflow
Install the official plugin or app. Search 'message.com' in your platform's plugin or app directory, click Install, paste your workspace key. The widget appears on your storefront immediately.
Custom site (HTML or any JS framework)
Copy the snippet from Settings > Widget > Install. Paste it before the closing </body> tag on every page. The snippet is roughly 30 lines, loads async, and adds about 18 KB to your page weight.
Google Tag Manager
If your site uses GTM, paste the snippet into a Custom HTML tag and set the trigger to All Pages. See /developers/tutorials/install-via-google-tag-manager for the full walkthrough.