Installing programs

Think of the .dmg files you download as a compressed disk. The disk that shows up on the desktop is the uncompressed disk and behaves exactly like a CD. If you install something off of a CD you copy it to your Apps folder and then eject the CD. You can eject the disk image the same way. The .dmg files are up to you to decide if you want to keep or re-download if you ever need to reinstall.

 

You dont need it once you have installed the app contained within. What you are seeing is a .DMG file. Its basically like an .ISO and it acts like a removable drive. i.e. you 'virtually' eject it.

When you have a .DMG file and open it. It will 'create' this icon you are talking about. All the info is contained in the .dmg file you clicked but the 'ejectable' part that pops up is how you access the content.

Thats putting it in basic terms because I only have basic understanding of it myself.

 

It's due to the way most Mac packages are shipped. They come as a disk image (think a 'virtual disk'). Once you've done installing the program you need to 'eject' the disk image.

As you've discovered you can either drag it to the trash can, or you can click on the eject icon next to the image name in the finder (it'll be in the top half of the left hand pane).