There are three sounds that "ed" makes when it is added to a word.
"t" "id" and "d"

The trick is to know when to use each one.

The sound "t" is used when the verb ends in these sounds:
"k" examples: tracked (sounds like track-t) and rocked (sounds like rock-t)
"ch"examples: launched (sounds like launch-t) and fetched (sounds like fetch-t)
"x" examples: waxed (sounds like wax-t) and boxed ( sounds like box-t)
"f" examples: laughed (sounds like laugh-t) and coughed (sounds like cough-t)
"sh"examples: wished (sounds like wish-t) and fished (sounds like fish-t)