what is difference between spam and trash

I assume you talking about email?

Spam is known junk or mail that is considerered to be 'unwanted' or unsolicited.

Trash is mail that you have decided to delete.

You have to mark messages as spam in Apple Mail to cause it to 'learn' about the items you do not want.

Both folders will need you to empty them, just select the folder & chose to delete from the Mailbox menu (or right click the folders & select from the popup menu).

No problem, lets see if this can be moved to the mail forums 🙂