If you desire something gratis and not complicated, Audacity is the first option that comes to most people's minds. It's available for Windows, Mac, and Linux, and takes care of simple cutting, noise removal, and effects quite efficiently. On the other hand, if you want a snazzier interface, Ocenaudio is less resource, intensive and quite easy for beginners. Should your editing be a bit more advanced and require multitrack work, Cakewalk by BandLab is very potent and still free on Windows. They are all great choices, depending on the degree of simplicity or advancement you prefer.