내리다 means "to go down", "to descend". This word is used together with 비 (rain), 눈 (snow) and other types of precipitation.

눈이 내려요 - snow goes down (it snows)

비가 내려요 - rain goes down (it rains)

Unlike English, there are no dedicated words in Korean that mean "to rain" or "to snow".

Moreover, verb 오다 (to come) can be used instead of 내리다 with the same effect. 눈이 오다 = 눈이 내리다