1. In a new column, enter the hire date for each employee.
2. In the next column, enter the following formula: =DATEDIF(B2,TODAY(),"y")&" years"
3. Replace "B2" with the cell reference of the hire date for the first employee.
4. The formula will calculate the number of years between the hire date and today's date, and display the result with the word "years" added at the end.
5. Copy the formula down to the rest of the rows to calculate the years of service for each employee.

Note: The DATEDIF function calculates the difference between two dates in years, months, or days. The "y" argument in the formula tells the function to calculate the difference in years. The "&" symbol is used to concatenate the result with the word "years".