Linking Fields From 2 Different Tables (Microsoft Access)
In your scenario, you have two 'entities':


Employees. These are stored in table Employee Details.
Schedules. Stored in table Schedules. A schedule stores an Employee ID and other information.


What you want to do is make sure that every schedule contains a valid Employee ID. That, you want to make it impossible to create a schedule with an Employee ID doesn't exist, and also to delete an employee from the Employee Details table if that Employee ID is currently being used in a schedule.

These requirements are handled by what databases call a foreign key constraint. In Access, you can use a graphical tool ('Relationships') to 'link' the Employee ID column in the Schedules table to the Employee ID column in the Employee Details table so that the constraints I described above are always met.

You can read up on foreign key constraints and Access' Relationships manager tool to accomplish this.