When we use the past simple tense and past participle for regular verbs they end in -ed.
Examples of past simple tense:
cook -> cooked
jump -> jumped
look -> looked
Keep in mind that many adjectives end in -ed because they are made from the past participle.
Examples of adjectives ending in ed:
He wears ragged clothes.
She likes painted nails.
We eat prepared meals.
How do we pronounce the -ed for regular verbs? We do it in three different ways:
Here is a table from English Club to illustrate how to make the sounds:
Here is a video on the ED Sound: