You will have to attach it to each employee.
Person --> Assignment --> Entries screen.
You can as well attach the accrual plan to all employees which satisfy an element link, by using the Standard Link functionality.
When you create an element link you can check the STANDARD check-box. this creates an element entry to all the employee assignments which satisfy the link eligibility criteria.
To view accrual entitlement balance you have to assign an accrual plan element to employee on element entries screen.
People->Enter and Maintain-->Assignment-->Entries
Also you can auto assign the accrual element to employees based on some eligibility criteria on element Link by checking the Standard Check.