Where is the head gasket on an Oldsmobile silhouette?

The head gasket on an Oldsmobile Silhouette (like most vehicles) is located between the cylinder head(s) and the engine block. There's one gasket for each cylinder head. Since the Silhouette uses a V6 engine, there will be two head gaskets. To access them, you'd need to remove the valve covers, various components on top of the engine, and then the cylinder heads themselves. It's a major engine repair job, not something easily described in a sentence or two.