The spark plugs on a 1998 Oldsmobile 88 (assuming it has the common 3.8L V6 engine) are located on
the top of the engine, under the plastic engine cover. You'll need to remove the engine cover to access them. They're arranged in a V-formation, following the cylinder arrangement of the engine.
Important Note: Accessing and replacing spark plugs requires some mechanical aptitude. If you're not comfortable working on your car, it's best to take it to a qualified mechanic. Incorrect installation can damage your engine.
