There is a difference between the words human and people. People is a collective noun, so it already refers to more than one person.
Human is a descriptive adjective or a noun. As a noun, it is singular and refers to one human being. So yes, you can say "humans", as in : He is a human; they are humans.
But, when using it as an adjective, you would always use the singular form, human. Ex: We are all members of the human race.
Hope that helps!