What is the rule of adding ed to verbs in English?

What is the rule of adding ed to verbs in English?

To solve this problem, I will give you a comprehensive and systematic talk about how to change the past tense of verbs in English, divided into two situations: regular verbs and irregular verbs
1. The changing rules of the past tense of regular verbs
1) Generally add ed at the end of the verb
work—worked,rain—rained,watch—watched