GMAIL supports POP3 or IMAP both so depending on your choice, you have to enable the related account option in your Gmail account (Gmail Settings -> Forwarding and POP/IMAP).
Now you need to start Outlook: from the main Outlook window, go to Tools -> Email Accounts (2010 or lower version) or AccountSetting -> add account (2013) After that addition of the account is self guided.
Few items to remember
1) Choose manual configuration.
2) POP Gmail servers for Outlook:
- Incoming mail server: pop.gmail.com
- Outgoing mail server: smtp.gmail.com.
- On the "Incoming server (POP3)" field, enter 995 as port number and mark the box "This server requires an encrypted connection (SSL)";
- On the "Outgoing server (SMTP)" field, enter 465 as port number and mark the box "This server requires an encrypted connection (SSL)".
3) IMAP Gmail server for Outlook:
- Incoming mail server: imap.gmail.com
- Outgoing mail server: smtp.gmail.com.
- On the "Incoming server (IMAP)" field, enter 993 as port number and mark the box "This server requires an encrypted connection (SSL)";
- On the "Outgoing server (SMTP)" field, enter 587 as port number and mark the box "This server requires an encrypted connection (TLS)".
