With aboslutely no idea what your database structure looks like, I'll have to guess....but a GROUP and COUNT will work.
SELECT
Year(EmployeeStartDate) AS YearHired, COUNT(EmployeeId) AS EmployeeHiredCount
FROM
EmployeeDetails
GROUP BY
Year(EmployeeStartDate)
ORDER BY
Count(EmployeeID) DESC
Assuming you've got a table with Employee details and always record their start date, you can use the YEAR function to group and count by that field. See if you can figure out how to select the record you're interested in.