Installing a software program writes the necessary data for running the program on your hard drive. Often the installer program will decompress the data included with the installer immediately before writing the information to your hard drive. Software updates, which are typically downloaded from the Internet, work the same way. When you run the update, the installer file decompresses the data and then updates the correct program or operating system.
Installing software is usually a simple process. It involves double-clicking an installer icon and then clicking "I Agree" when the license agreement pops up. You may have to choose what directory on your hard disk you would like to install the software in, but often the installer will even choose that for you. Some software can be installed by simply dragging a folder or application program onto your hard drive. Either way, installing software is a rather simple process and should not be intimidating. If you can cook you dinner in the microwave, you can install your own software.