There are two types of patent infringement, direct and indirect. Direct infringement occurs if you make, use, offer to sell, sell or import any patented invention in the U.S. without authorization of the patent holder. Indirect infringement occurs in two scenarios. First, you are guilty of induced infringement if you induce someone else to infringe another person's patent. Second, you are guilty of contributory infringement if you offer to sell, sell or import a component of a patented invention, and know that the component will be used for infringing purposes.
Direct infringement is a strict liability tort, which means you can be held liable without intending to do anything wrong. Induced and contributory infringement are not strict liability torts; both require the alleged infringer to know he or she is doing something wrong.
If the claims of a patent cover a product or apparatus, direct infringement will always be present. If a patent claims a method (method patent), you can also have divided infringement, which is a type of induced infringement. With divided infringement, a defendant can be held liable if he or she performed some steps of a claimed method and had others do the remaining steps, or if he or she had others to collectively perform all of the steps of the claimed method but no single party did all of the steps individually.