With Google Sites you do not need to add code to your site, just the Tracking ID. If you get stuck request the Google Analytics Configuration Service
Once you can see the What do you want to track page use the large Website button (not App) and:
Once you finish entering all this information use the blue
Google Analytics will now give your your websites Tracking ID that looks like UA-123456789-1 (yours may be longer or shorter) and you can find it highlighted in blue on the screenshot on the right.
Use the blue Save button and you're finished in Google Analytics
Return to your Google Site and now use the More button then choose Manage Site and go to the General tab
Once in the General settings check the Statistics tick box and enter the Tracking ID in the Paste your Analytics Web Property ID here: text box.
After 24 hours you should start to see data in Google Analytics.
We can offer training on how to get add Google Analytics to your Google Site and how to get the best out of Google Analytics (like the best reports to use and what to do about the statistics Google Analytics gives) via Skype or Google+ Hangout through our one-shot support service.
Make you you have correctly registered your Google Site in Google Webmaster Tools, so your Google Site can get found in search engine result pagesGoogle Sites adaptation of Google's SEO Guide for more advice on how to make your website more accessible to your visitors and search engines - Google Sites - SEO (Search Engine Optimization) Guide.