Your Gmail can be delegated to another user, which allows them to access your mailbox without the need to know your password. Delegated user is mostly used for shared mailboxes (sales, support etc.). Delegation only affects Gmail and no other Google services are delegated. Delegation can only be done between accounts in the same organization.
1. Open that Gmail's setting which you wish to delegate and navigate to Account tab
2. From the Grant access to your account click Add another account
3. A new window opens. Write the user you would like to delegate the access to and click Next Step
4. From the next page click Send email to grant access
5. Whoever has access to the account that was granted the access needs to accept the delegation by clicking on the accept link from the confirmation email
6. After confirming the delegation, the other user can now access the delegated account's Gmail from their own Gmail by clicking their profile picture from the top right corner