The word "least" is the opposite of "most." It describes an amount that is smaller than other amounts.
Of the three choices, she likes the orange one the least.
Joe puts the least amount of effort in getting his work finished. He’s very lazy.
That was one of the least interesting classes I have ever taken. It was very boring.
Finding a new job is the least of her problems. She has many other problems to deal with.
The least amount of pain and suffering happened at the beginning of the war; most of the war’s devastation was felt towards the end of it.
The preposition "at" is often placed in front of "least" to form "at least." This is a kind of idiom that we use to describe some advantage despite a difficulty.
Tom has a difficult job. At least it’s interesting.
Their company went out of business. At least everyone received one final paycheck.
The party was held under a very cloudy sky. At least it didn’t rain.
…but at least he still has his donkey.