Firstly, to be able to set up Gmail on Outlook, IMAP has to be enabled on your Google account:
Google may block sign-in attempts from some apps or devices that do not use modern security standards. Since these apps and devices are easier to break into, blocking them helps keep your account safe.
Some examples of apps that do not support the latest security standards include:
If you want to change your account security settings to allow these apps despite the risks, use the following steps:
Now to setup Gmail, if this is a brand new email account, skip to Step 10. If you currently have an existing email account with the same email address already set up in your Outlook, use the following steps:
If you have set up your mailbox through Control Panel in the above steps, skip to Step 12
Congratulations! You can now access your Gmail through Outlook 2016.