Automatic settings
If you want to add a personal Gmail account, you must activate IMAP support first. See Google's documentation for more details.
Add the account to Outlook. Chose "File", "Add Account"
Type your name, external email address and the password to your account.
Outlook will automatically detect the correct connection settings and add the account.
Your email account will now be shown in the list of folders on the left side.
Manual settings
If Outlook is unable to detect settings for your account automatically, you can add it manually. Look up your email provider's documentation to find the details of what settings to input.
Calendar
You can subscribe to your private Google calendar in Outlook. This way, you can keep track of both your private and professional appointments.
Read Microsoft's documentation on how to subscribe to a Google calendar in Outlook