Cannot empty trash after deleting .dmg

So, I downloaded Chrome, and I put it in the Applications folder and from there a shortcut to the applications bar on the bottom of the screen. All is fine, but now there's an icon on the desktop that looks like a harddrive with a Chrome icon on it. I don't want it there, but I don't know what to do with it. I also have the DMG file from the download in the Trash, but it won't let me delete it.

So, how do I get rid of the downloaded file which I thought was 'installed' in the Applications folder?
Also, how do I get rid of the Chrome HDD icon on the desktop.
And, in the end how many copies of an application does OS X keep just to make it work? It's rather annoying coming from Windows, where there's only one...

Anyway, help would be appreciated!

Solution 1:

The hard-drive looking thing on the desktop is a mounted disk image; the .dmg file is the file where the data for the image is.

To get rid of the image, unmount it. There are three four five good ways to do it:

1. Drag the disk to the trash. The trash will turn into an eject icon while dragging.
2. Highlight the disk on the desktop and select File > Eject in the Finder menu bar.
3. Highlight the disk on the desktop and press Command-E.
4. In any Finder window, press the Eject button next to the disk in the sidebar.
5. Right-click (or control-click or two-finger-click) on the icon and select Eject. (from JoshHibschman in the comments below)
6. You can also eject from the commandline using diskutil if you really want.

After you eject the disk

Insofar as the application "file" is concerned, there is only one copy of the application: the one in the /Applications folder. The icon in the dock is only a link (not really a shortcut, as there's no file like a shortcut in the Start menu or the Quick Launch bar, but it's not bad to think of the Dock icon as a "shortcut".)

And to answer your first question, this is a great place to come with questions. Hope you have a good time on the Mac!