By default it is required that you close your current session to open another under a MAC. But it is possible to switch to another session without closing the actual one session.
- Go to "System Preferences."
- In the "System" select "Accounts."
- A window appears, click "Options."
- To make your changes, click on the padlock and enter your password.
- Check the box to the left of "Show Fast User Switching menu as:".
As from now all users account will be displayed in the taskbar. To switch to another user, simply select it from the list.