Waves transfer energy and are made up of pulses. There are two main types of waves: transverse waves, where particle movement is perpendicular to velocity, and longitudinal waves, where particle movement is parallel to velocity. Longitudinal waves have two parts - compressions where particles are closer together, and rarefactions where they are farther apart. When two waves meet, their amplitudes add through interference and superposition, which can make the combined wave bigger or smaller.