The SIMPLE PAST TENSE

The PAST TENSE indicates that an action is in the past relative to the speaker or writer.

when the time period has finished: "We went to Chicago last Christmas."

when the time period is definite: "We visited Mom last week."

with for, when the action is finished: "I worked with the FBI for two months."

Regular verbs use the verb's base form (scream, work) plus the -ed ending (screamed, worked). Irregular verbs alter their form in some other way (slept, drank, drove).
Students for whom English is a second language sometimes (quite understandably) have trouble distinguishing between the Simple Past and the Present Perfect tenses. There is more information about the difference between these two tenses available under the Present Perfect description.

Singular	Plural
I walked	we walked
you walked	you walked
he/she/it walked	they walked

Singular	Plural
I slept	we slept
you slept	you slept
he/she/it slept	they slept

Singular	Plural
I was	we were
you were	you were
he/she/it was	they were

When I was a girl, I walked five miles to school every day. 
Carmelita slept through the entire class. 
We worked really hard to make this a success, but then Chuck ruined it with his carelessness. 
Every time I finished a sandcastle, the waves came in and washed it away. 
Tarzan dove into the swamp and swam toward the alligator.