No single element of the Macintosh interface is as recognizable or famous as the trash can icon, which appears at the end of the Dock. (It’s actually a wastebasket, not a can, but let’s not quibble.)
You can discard almost any icon by dragging it into the Trash can. When the tip of your arrow cursor touches the Trash icon, the little wastebasket turns black. When you release the mouse, you’re well on your way to discarding whatever it was you dragged. As a convenience, OS X even replaces the empty-wastebasket icon with a wastebasket-filled-with-crumpled-up-papers icon, to let you know there’s something in there.
It’s worth learning the keyboard alternative to dragging something into the Trash: Highlight the icon, and then press ⌘-Delete (which corresponds to the File→Move to Trash command). This technique is not only far faster than dragging, but it also requires far less precision, especially if you have a large screen. OS X does all the Trash-targeting for you.
If a file is locked, a message appears to let you know; it offers you the chance to fling it into the Trash anyway. That’s a better solution than in older versions of OS X, when you were forced to unlock the file before you could trash it.
File and folder icons sit in the Trash forever—or until you choose Finder→Empty Trash, whichever comes first.
If you haven’t yet emptied the Trash, you can open its window by clicking the wastebasket icon once. Now you can review its contents: ...