You can create a multiple user accounts and enable fast user switching. To do this go to system preferences and open accounts. Now authenticate yourself by clicking the lock icon to be able to make changes. Now click + button and fill the new account information like name, password etc. All user have their own different user folders to put files. Also you can give authority of admin to any user by clicking "allow user to administer...." Now to login with different user account you have to go to the apple menu and click log out but when you log out your running applications will be closed. To avoid it you need to click login option in account preferences and enable the fast user switching by clicking the box of the fast user switching option. Now you will get this menu in upper right hand corner to switch between users without closing your applications. You can also enable a guest account. When guest account log out all its files and settings will be deleted. If you check your hard drive you can see the all user's folder there.