Explain Download Volumes and Mountpoints?

Hi, I was wondering if anyone out there could explain the download process to me. When I download software, the 'volume' appears on my desktop, I drag the app to the app folder, the volume is still there. Do I need it?

Also, I was wondering about the mountpoint. What exactly is it? Just the place that the app was installed to?

Then, if I install something that doesn't work, how do I un-install it? I tried to install a php version that was supposedly specifically for OSX. It isn't working. I'd like to un-install and try again. How do we do that?

Would appreciate any help on this....

Thanks.

If you have copies an application to your local applications folder, then you can drag the volume to the trash to unmount it

MOuntpoint? I assume you mean that volume that appears. Its the default way to install OS X apps, like a virtual drive. Once you have copied the app to your local drive then they are not needed.

Thanks for the help. I guess my biggest 'worry' was if I have to do some sort of cleaning process before I try to re-install, or if just dragging the app to the trash would get it all.