Which were the different methods of …

Gandhiji believed that the British empire in India could survive as long as the local people were cooperating with foreign rule. Non-cooperating with the British government was to weaken it and also to protest against the same. Following points explain how it was a protest:

1. Non-coperation movement came along with the Khilafat movement, The British has not seen Hindu Muslim unity of this level ever in history. The protest of the people was unified cutting across communities and at great scale.
2. People boycotted the pillars and symbols of British rule, courts, colleges and government offices. Lawyers stopped going to courts and students stayed away from colleges. At many places, alternate arrangements were done to solve litigations out of court. Further many education institutions were established by the leaders of freedom struggle where students can study. One of them is Jamia Millia University in Delhi which exits today as one of the most reputed seats of higher education in India.
3. People boycotted tax collection also and they refused to pay taxes.

Thus, non-cooperation was a kind of protest too.