By 36 months old, most children talk about nearly everything in their world using nouns, verbs, adjectives, pronouns, and prepositions. They will use 3- and 4-word sentences to describe and request. They are now usually able to use more speech sounds correctly, and their speech can be understood at least 75 percent of the time.
Also by 36 months old, you should notice that your little one understands more complex language such as opposites and prepositions. By this age, children should be able to answer a variety of wh- and yes/no questions as well as follow 2-step directions. Attention to books will increase to longer periods of time, and they usually enjoy more complex stories.