You are probably thinking of the preliminary notice. This is a necessary pre-lien notice to the owner and/or contractor that there is a sub working onsite who will demand to be paid or else will have the right to put a lien on this property.
Do I need to let the contractor/property owner know before I put in a preliminary notice? Or can I just put it in?
No you don't need to let them know before you issue the preliminary notice. They find out when you issue it. You have to follow the rules on where to send it-- to the owner's address, post it at the job site maybe, send to the GC. It depends on who you want to force payment from.