This is a little guide on how to correctly install an HP printer, since so many people seem to have trouble with this. I have also provided a very basic scanner start up guide. Here are the steps:
First of all, connect your printer to your computer, and turn it on.
See if your printer gets autodetected by Ubuntu. If it does, something will pop up saying it is configured for use and is ready.
If nothing happens, simply go to System > Administration > Printing > New.
If it doesn't find any or doesn't recognize your printer, try the official hplip website to try to download the correct drivers for your printer.
If even that doesn't work, then post here with your printer name and configuration, and maybe I or someone else can help you.
For HP all-in-ones (such as the PSC series), after you have followed the above steps, put the paper you want to scan in the scanner and then go to Applications > Graphics > XSane Image scanning program. In XSane, click "scan" and then when it's done, click save as and save it wherever you want.
If you have a sole HP scanner, then you could try to just plug it in, turn it on, and try to scan it with XSane, but I don't gurantee that it will work.
***NOTE: If you want to send a scan that you made on your linux box to a windows computer, it won't open it up (I don't know why, it just wouldn't for me). You have to right-click on the image, and go to "open with GIMP Image Editor". Then go to save as and click on "select file type (by extension)". Then scroll down to JPEG format and click ok as many times so that it saves. It'll then be readable in windows.