If you don't have a hard disk, then there is no installation procedure. It might be wise to make backup copies of the floppy disks though.
If you have a hard disk and want to install PLPLOT on it I recommend creating a :plplot/lib directory on your harddisk and then copying the library there. The following commands will do the trick.
makedir HDDISK:plplot/lib copy plplot1:lib HDDISK:plplot/lib allBe sure to substitute the name of your own hard disk for HDDISK in the above commands.