This feature is exclusive to PREMIUM or PLATINUM accounts, which can have up to 5 and 25 user profiles respectively. If you are a BASIC user and wish to benefit from this feature, please upgrade.
You can add and manage User profiles under the Settings tab of your account.
Click on Users on the left hand side. To add a new User profile, click on the blue "NEW USER" button.
In the window that opens, enter the information to create your User profile. Select the access you wish to give the profile in the Access tab. 
You can modify a User profile at any time. Click on the Pencil icon next to the User you wish to edit to update profile information and access. 