In order for your teachers to be able to reconcile lessons and view their calendars, you will need to create accounts for them. It's easiest to do this when adding a teacher, by simply filling in the "Login Information" section of the "Add Teacher" form.
But you can also create a teacher account after the teacher has been added. To do this, go to the teacher list under the "Employees" tab. Click on the row of the teacher for whom you want to create an account. In the "Login Information" section in the right column, give the teacher a username and password. Now they can access their account.