Regular verbs add -ed. The form never changes with the subject, so there is no -s to worry about.
| Rule | Verb | Past simple |
|---|---|---|
| Most verbs: add -ed | work | worked |
| Ends in -e: add -d | live | lived |
| One vowel + one consonant: double it | stop | stopped |
| Consonant + y: y becomes -ied | study | studied |
Use the past simple for a finished action at a finished time, very often with a phrase saying when: yesterday, last week, in 2019, two hours ago.