You'll notice in the lists below that many Alexa skills are called by using trigger words like open, start, play and ask. While select skills require you to use specific terms, others consider them to be interchangeable and will work with some or all of these phrases. Over time you'll begin launching your favorite skills by the words you feel most comfortable using. Initially, though, it can be fun to play around with each.
Warner Brothers created a choose-your-own-adventure game for Alexa called The Wayne Investigation, wherein you investigate the death of Bruce Wayne's parents, Thomas and Martha Wayne. Start the game by saying, "Alexa, open The Wayne Investigation" and follow the prompts. Each choice you make affects the outcome of the story. This is one of the best examples of a game style that suits Alexa perfectly.
Like all AI devices that use National Language Processing or NLP, Alexa does not understand all voices easily. But she learns to understand her people over time. She does, however, require people to speak in simple terms, with appropriate pauses, and use specific word orders. There are many times when she will say "I'm sorry, I don't know the answer to that question." More than likely, she doesn't recognize a word order or misunderstood the question.