The instructions for configuring your MX records with Google Mail can be found directly at Google: How do I set up Gmail for my domain?
These records must be updated with your domain host, not the Google Admin console. Each record you configure to your domain’s DNS setting will point to Google’s mail server. Here is a copy of the values you will need to configure your domain’s MX records with Google Mail:
The TTL (time to live) is the number of seconds it will take for your changes to the MX records to take effect. A TTL value of 3600 will ensure the records propagate within an hour.
The Priority reflects the priority of the Google Mail servers for each record. Mail is delivered to the server that contains the highest priority first. If the server is not available, mail will be delivered to the server with the second highest priority and so on. The records with the lowest number will be the highest priority.