Mahatma Gandhi travelled to Champaran in Bihar in 1917 to inspire the peasants to struggle against the oppressive plantation system. The peasants there were forced to grow indigo and other crops under harsh conditions imposed by British planters, and Gandhiji used satyagraha — non-violent resistance — to support their cause.
The source directly states: "In 1917 he travelled to Champaran in Bihar to inspire the peasants to struggle against the oppressive plantation system." Examiners expect you to mention (1) the reason — oppressive plantation system — and (2) the method — satyagraha/non-violent resistance. Do not confuse Champaran with Kheda (Gujarat) or Ahmedabad (mill workers), which were separate movements.