The regular way to talk about finished actions
One ending turns a regular verb into the past - when to use it, and how the spelling shifts along the way.
Last night I watched a film and then studied for two hours.
Regular verbs mark a finished past action with a single ending, the -ed form, and the same form works for every subject. Use it when the action is over and the time is stated or clear from context - yesterday, last week, in 2019. The spelling adjusts in two common cases: a short verb ending in one vowel plus one consonant doubles that consonant, and a verb ending in a consonant plus the letter y changes the y to i before the ending.
In negatives and questions, the past marking moves onto the helper verb, so the main verb goes back to its base form - keeping the past ending on both is the classic error at this level. Watch the spelling traps too: the doubling and the letter change happen only in their exact cases, not everywhere.