When you click on the My Subjects tab if you can not see your class/subject then this would indicate that you are not assigned to the class.
This will need to be fixed by a member of staff with the Admin Role.
Firstly go to Admin > Classes.
>> 
Next click on the Add Teachers To Class Tab.
Then find the staff member from the dropdown and choose which year group they teach and click choose.
All you need to do now is tick which classes they teach to allocate them to it.
Once you have ticked the classes they will show under the Current Allocation area.
You can use the red crosses to unassign staff from classes.