Hi! 1. Swapping one thing (action) to another thing (action) ---> На смену теплому лету пришла прохладная и сырая осень; 2. Group of workers who work during the certain gap of time (night shift, for exmp) ---> Ночная смена трактористов :) 3. Set of clothes which can be changed each other periodically ---> Две смены белья

Смена has several meanings. Literally it means - replacement. However, usually we use this word when we are speaking about "shift". For example: I work in night shift. Я работаю в ночную смену. An additional example with a different meaning: We have changing seasons during the year. Смена времен года.

One more meaning: a younger generation of people who are supposed to change the older ones in a certain field or follow the same interests. f.e. Растет достойная смена олимпийским чемпионам.