With regular verbs you make the simple past by adding '-ed'.
Unfortunately, there are a number of irregular verbs and with those, this rule doesn't apply.
The irregular verbs have their own form that you have to memorize/study.
present tense |
past tense |
to be |
was/were |
to buy |
bought |
to come |
came |
to do |
did |
to drink |
drank |
to eat |
ate |
to feel |
felt |
to find |
found |
to get |
got |
to give |
gave |
to go |
went |
to know |
knew |
to leave |
left |
to make |
made |
to meet |
met |
to read |
read |
to say |
said |
to see |
saw |
to sit |
sat |
to sleep |
slept |
to take |
took |
to teach |
taught |
to tell |
told |
to think |
thought |
to understand |
understood |
to wear |
wore |
to write |
wrote |
You can find various lists of irregular verbs on the internet.