You can save space on a computer hard drive by installing software on an external hard drive instead of the PC's hard drive and accessing it from the external hard drive.
While this is an effective way to save space on a hard drive, do not assume that software installed on an external hard drive will be portable. Some simple programs may be able to be transferred to other systems this way, but a more complex program will have certain components installed on the main PC and will not be recognized on other systems.
Connect the external hard drive to the PC via USB connection. Turn the external hard drive on.
Begin the installation process for the software and follow the installation prompts.
Choose a destination drive to install the program onto when prompted. Select the drive that corresponds to the external hard drive.
Continue the installation process, and the software should install on the external hard drive without problems.
Never attempt to disconnect the external hard drive from the PC while programs are running that are installed on the external hard drive. This will result in numerous errors.
If this is attempted, be aware that some software that may run from an external drive will create error messages on the PC if the PC is booted up without the external hard drive being connected.