What the past tense of the word help?

Help is a regular verb. This means to make the past tense form you simply add -ed to the word
help -- helped
Past tense has has several forms:

past simple -- I helped at the cinema last night.

past continuous -- They were helping me find the torch. He was helping with the lights.

past perfect -- I had helped him three weeks before.

past perfect continuous -- I had been helping James when the siren went.