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How to add and edit admin users and user roles in Magento
In addition to the admin account that's created while installing your Magento you can add more users that can access the admin panel. You can determine what these users are allowed to do by assigning them to a user role with specific permissions.
First, you need to create a user role and configure its permission settings. To do this in the admin panel go to System>Permissions>Roles. On the following page there's a table with the existing roles which you can edit by clicking on the name of the role. By default, there's one preconfigured role that gives full access to the admin panel. To add a role click on the Add New Role button. On the next page specify the name in the field for Role Name, then click on the Role Resources button on the left. This will show on the right a list of all the actions and settings available in the admin panel. Next to each action/option there's an empty checkbox. Mark the checkboxes for the actions/settings to which you want users belonging to that role to have access. After that click on the Save Role button in the upper right corner of the page.
After you create the role you can assign it to new and existing users. To add and edit users go to System>Permissions>Users. On the page that opens there's a table with the existing users. To edit a user click on the respective row in the table. To add a new one click on the Add New User button in the top right corner. On the next page type a username, password and all the rest of the user information in the respective fields. Then click on the User Role button on the left. A table with the existing roles will appear on the right. Mark the radio button for the role to which you want the user to belong and click on the Save User button in the upper right corner.
For some more information and screenshots you can also read the tutorial on how to manage admin users, permissions and user roles in Magento.