When did it start anf why?

Lent actually started about 300 years after the death of Jesus. At that time many converts were baptized in water on the day set aside to celebrate Jesus' resurrection. To prepare them and others who desired to be ready for this great celebration, they would "fast" from certain delicacies
( or acts ) for 40 days prior to the celebration. It is not in Scripture, or any command of God, but man's desire to put their attention on spiritual things for this period of time. ( 40 days were chosen probaly because of Christ's 40 days in the wilderness.)