When two or more waves are in the same phase, they are said to interfere constructively or that they have constructive interference. In comparison, when waves are out of phase, they are said to interfere destructively. When waves have constructive interference, the resulting wave will have greater amplitude than either of the participating waves. When waves have destructive interference, the resulting wave will have lesser amplitude than the participating waves. For example, when someone throws a stone in water, we see some waves travelling away from point of impact of stone. If someone were to throw another stone, in the vicinity of the first stone, around the same time, the waves will interact with each other and resulting wave may be larger or smaller than these waves, depending upon the nature of interference. Similarly, we notice that when two different types of sounds are generated, the effect may pleasing (as in the case if music) or irritating (vehicle horns, etc.). Hence in phase or out of phase waves, constructive or destructive interference, may cause interesting effects in waves.
Hope this helps.