Can someone tell me what the following codes are in order to install autocad on a computer.....I am thinking about installing a used older version:
Answer depends on how "old" of a version this is. Regardless, even if you do get it installed, you'll need the S/N at some point and you'll need to activate it with Autodesk.
You should have the S/N from when you purchased it. IF not, nobody here can help you other then to point you to Autodesk or back to the reseller from who you made the original purchase.