The word other can be used as a determiner or a pronoun.
When used as a determiner, other is followed by a plural noun.
- Besides Peter, she has three other children. (NOT She has three other child.)
The other can be followed by a singular or a plural noun.
- She lives on the other side of the street.
- Where is the other book you borrowed from me?
Other can also be used as a pronoun. In this case, it is usually preceded by the article the.
- She walked from one side of the road to the other.
The plural form others can be used with or without the.
- Some students are smarter than the others. OR Some students are smarter than others.
The word other is used to refer to additional people or things of the type we have already mentioned about.
- Have you got any other cellphone models?
- Where are the other boys?
Note that when other is followed by a noun, it has no plural form. But when it is used alone without a noun, it can have the plural form others.
- Where are the other books? (NOT Where are the others books?)
- He has already returned some books. Where are the others? (Here other is used alone and hence it can have the plural form others.)
- These shirts are too small for me. Have you got any others?
Note that other or others is only used alone when it refers to a noun that has already been mentioned.