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:
/ɪd/
/t/
/d/

Here is a table from English Club to illustrate how to make the sounds:

Here is a video on the ED Sound: