In previous version of OS X, installation software for various printers come pre-loaded. This usually adds up to having files for hundred, if not thousands, of printers from the different brands. And you do not really use all of that. The average user will probably just connect one or two printers to his Mac.
In an effort to have a smaller footprint and be more compact, Lion did away with all of these and would now install on as-needed basis, specific to the printer being connected. It helps that printers nowadays are physically connected via USB, making it easily discoverable. Networked printers are also easy to install.
To install your preferred printer, connect your printer to your Mac. Power it up. Lion will search for your printer. If you have a specific document to print, open that. If not, just choose any file. Click Print from the File menu or tap Command-P. If your printer is already installed, then it should be available for selection in the Print pop-up menu.
On the off-chance that Lion cannot auto-detect your printer, you can manually add it yourself. Press Command-P and wait for the printer menu to pop up. Select Printer and click on Add Printer. A setup window should appear, listing all the printers in Lion’s database. Select your printer and click Add. You’re good to go.