You can use whatever and how many levels you want or need depending on your application. The above is provided as a basic example. You can also add more fields to tblUser if needed.
Once you have the tables setup, you can create the Login form. This will be an unbound form with two controls; a combobox to select the user and a textbox to enter the password. You will want to restrict this form by turning off the Min, Max and Close buttons. Also set the Navigation Bar and Record Selector properties to No. I suggest the name frmLogin for the form, cboUser for the combobox and txtPassword for the textbox.
For the combobox, you will set the ColumnCount to 5, the ColumnWidths to 0;1;0;0;0 and the RowSource property to the following SQL statement or create a named query: