this is saying that you are linking the table or query Times to the table or query Appointments on Timeslot=Appointment time
Enforce referential integrity means that you cannot have a record in appointments without a 'linking' record in Times as above
Cascade Update related fields means that if you change the timeslot value in times, it will change the appointment time value in appointments
Cascade Delete related records means if you delete the record in times, it will delete all the related records in appointments which have that timeslot