Go to Gmail.com and log in. Once you have logged in, on the upper right hand side there is a cog next to arrows, press it. A menu should open; on that menu press Settings.
On the Settings page click the Accounts tab and look for the "Grant access to your account" section. On this page you can add other emails to see your emails, and also add another email address.
Select "Add Another Account" and a window should open allowing you to type in an email address. After entering an email address, click Next Step.
You can only do this if you are allowed by your work or school. You can freely do this to your personal email.