Add the same tracking code to all pages
If you'd like to add the same code in the header (or footer) of every page in your site, simply use the Tracking Codes page. Find this by going to Dashboard > System & Settings > SEO & Statistics > Tracking Code.
Add tracking code to just one particular page
If you need to add different snippets of tracking code on different pages, you're in luck: concrete5 has a custom page attribute that is installed by default. It's called Header Extra Content, and it's located in the Page Header attribute set.
Navigate to your page (or find it in the Sitemap), then go to Page Properties > Custom Attributes and click "Header Extra Content" from the list of available page attributes. Paste your tracking code in the text field that appears on the right, click save, and you're all set. The code you've entered here will be included in the headers for this particular page.