Setting up Google servers on a domain is very easy and does not require any prior knowledge.
1. Select the desired domain in the management interface and select: DNS and MX
2. You will then see a screen like this on the right side of the screen:
3. Note the two values: Primary MX address and Other MX (backup) servers. Currently, the first is set to Default and the second is empty. This indicates that the domain's MX is configured for the server.
4. Let's change the desired values. Change the Default to aspmx.l.google.com and the second to alt1.aspmx.l.google.com, then click on the V (Confirm) at the bottom. Please note: Unlike other panels, there is no need to enter the dot (.) at the end, as shown on Google's website.
5. After clicking on the V (Confirm), a new line will appear under Other MX (backup) servers. Enter the third value: alt2.aspmx.l.google.com and click on V (Confirm) again.
6. Continue entering the new line we received and click V until you have entered all the MXs we received from Google. The list of MXs can be found here: https://support.google.com/a/answer/174125
Good luck!