What is verb 1?

It sounds like you're asking about patterns like "see - saw - seen", or (Brad's example) "go - went - gone". Basically, the past participle ("verb 3") always needs a helping verb. Always. It can't function without one. So you can say "I have seen" or "it is gone", but "it gone" and "I seen" are completely wrong; you need "it went" and "I saw" (simple past) in these cases. You use the past participle in perfect tenses (I have seen; I had eaten; I will have spoken), hypothetical forms using "have" (I should have known; it could have sunk), or passive forms (it is known; that was eaten). Verb 2 (past simple) is the basic past tense of the verb.

Are you talking about the simple past (e.g., "went") vs. the past participle (e.g., "gone")?