They didn't have lawns. They had gardens of course, and, they kept areas cleared of trees (for example around castles, so you could have a line of sight to attackers) etc. But large swaths of manicured grass are an English and French invention from the 16th century.

Using a scythe + a rake. Additionally, animals such as sheep could be used. Needless to say, lawns were typically reserved for the wealthy, where this intensive labor could be offloaded onto servants.