Mac OSX and dmg files?

Double click the .dmg file and it will mount to the disk. The contents will open and there should be either an installer or the .app file. The installation will automatically put the application into its proper folder, and the .app file can be drug to the folder. Once the .app file is actually on the hard drive (the installation/drag and drop), unmount the .dmg by click the little arrow next to its name in any Finder window. The original .dmg can be deleted and the application is safely tucked away in the applications folder.