Hi Sinem, you could say:
He didn't wear a life jacket on the boat yesterday - this is the negative of "he wore a jacket" (past simple)
He wasn't wearing a jacket on the boat yesterday when the boat sank - this is the negative of "he was wearing a jacket" (past continuous)
The second one is used when you are describing an action when something happened because we assume that the action of wearing the jacket started before something happened and continued after it.
I hope this helps.