OS 3.9 question

[Steady]

'installer' is not in your path. Check to see if it is actually on your system somewhere (I think it is in Utilities or C normally) and ensure there it is in the path set up by the startup-sequence. It is probably in utilities as if it was in C there is unlikely to be a problem.

The alternative is to change the default tool type on the icon you are clicking to point to the full path (eg: SYS:Utilities/installer, assuming it is actually in that location). That could potentially be a real pain. Ensuring it is in your path is more effective.

[Steady]

FallenOne has given you a link to all you should need, though I thought 3.9 came with it's own installer ... Check the CD if you have it, too.

BTW. The "install" command in the C: directory is for installing bootblocks onto floppy disk and is completely unrelated to program installations.