An integral part of world building is, of course, the people that make it up. Where would your world be without sentient life-forms of some sort, either alien or familiar? However, within that hierarchy there are many different kinds of people, and some are less familiar than others.
However, is there even a need for a race other than mankind in storytelling? Unless you are writing CRF, the answer is usually an outstanding yes. The reason? Simple: the idea of sentient beings existing apart from humans pose some very interesting questions, both moral and scientific.
Man fears what they do not know. Therefore, the race that is most alien to them is the one they fear most. As such, many writers have used races foreign to mankind to terrify them. Other races can aid humanity. Races can be humanoid, foreign, tiny, or gigantic. They can be friends with humanity or enemies thereof. Sometimes, humanity doesn’t exist and other races are all there is.
Definitely, sentient races other than humanity have tremendous uses in a story. With a little creativity and a little inspiration from real life, you can make use of this device as well. Alternate races can be used in a multitude of different genres of books, but most notably they have been used in science fiction and fantasy.
One cool element that other sentient races can possess is that they don’t necessarily need to be in the story. They can enrich the story, make it better, forge part of the plot, but in the end you can make it so that the other race is not vital to the story. However, if you can make it a sort of “cool add-on”, that works in your favor as well.
However, how do you create another kind of people in the first place? The best way is to ground your inspiration in reality: maybe your new race is a myriad of gladiatorial space aliens, all warlike and brutal. Your inspiration? The ancient romans with a dash of your own ideas.
Maybe your race is a group of casual, insectile nomads. They are merchants, and a few of them are petty thieves. They can interact with humanity and have their own language, but they care little for social interaction and a lot about foreign currency. My inspiration? My grumpy, miserly neighbor who lives next door. Heck, their leader is even named after him.
You have to learn to take inspiration from everything in real life, and this is no exception. Base your prime inspirations for your nonhuman race off things you see in real life.
Now, you need a hierarchy. Something to make your culture come alive. What are their likes and dislikes? What must they do to survive? What is their system of government, if anything? What is their history? (That’s a big one.) If something can be known about a real group of people, research it and find out. Specify all that you can.
Once you’ve got your nonhuman race established, then what? Well, tell your readers all about it. Make some of your main characters this new race of sentient beings. Feel free to explore moral problems, questions like are these new “people” truly people? Stuff like that.
Good luck, and happy writing!