Step 1 - Adding A records
A records that you need to create at the domain’s DNS Zone:
Points to: 188.8.131.52
Points to: 184.108.40.206
Points to: 220.127.116.11
Points to: 18.104.22.168
The result will look like this:
Step 2 - Adding a CNAME record
You only need 1 CNAME record with the following values:
Points to: ghs.googlehosted.com
It will look like this:
After that, you will need to verify your domain (STEP 3) with Google, it might take up to 4 hours to Google recognize your changes and accept your new domain.
And it's done! Now just wait for propagation and your website will work with Google Sites.
If these records for the same host values were already added, you need to delete them before adding new ones.