You know, I like this word very much because it functions as a verb and as an adjective, besides it can mean so many meanings.
Here you are some: to save, to waste, to free, have something extra, something you do not need any more, prevent someone from experiencing something bad.
Now I can think of some exemples to make things clear:
*I have to spare some money to offer my friend a birthday-gift.
*The exams are so near, I have no time to spare.
*You can spend the night here, we have a spare room in this house.
*I cannot provide spare sandals this summer.
*The prisoner was spared the penalty.
Can you find more meanings and exemples?
Correct me if I am wrong