Regular verbs form their past tense by adding "d" or "ed", while irregular verbs do not follow a pattern and must be memorized. The document provides examples of forming the past and present/past perfect tenses of regular verbs like "share" and "pour" by adding "d" or "ed" with a helping verb. It contrasts these with irregular verbs like "see" which has the forms "see, saw, seen". A table lists common regular and irregular verbs along with their present, past, and present/past perfect forms to help with memorization.