There are different types of indefinite pronouns and each type is used in a slightly different way.

Assertive indefinite pronouns, also known as assertive existential pronouns, refer to an unspecified set of people or items with a specific or known feature. Assertive pronouns are mainly used in affirmative sentences and can act as subjects and verb complements in sentences. Here is the list of assertive indefinite pronouns:

Assertive indefinite pronouns 'someone' and 'somebody' are used to refer to a person whose identity is either unknown or unspecified.
'Someone' is slightly more formal than 'somebody'. Otherwise, they are used interchangeably.

'Something' is an assertive indefinite pronoun that refers to a thing or an object when its name or identity is unknown or unspecified.

Non-assertive (also called elective existential or elective/dubitative existential) indefinite pronouns select an unknown set of people or things without specifying their features. These pronouns are mainly used in negative statements and questions and function as verb complements but not subjects. Here is the list of non-assertive indefinite pronouns:

'Anyone' and 'anybody' refers to a person whose identity is not important.
'Anyone' is slightly more formal than 'anybody'. Otherwise, they are used interchangeably.

'Anything' is used to refer to an unspecific object, event, situation, etc., without mentioning a particular feature or criterion.

Universal indefinite pronouns include all items in a list, regardless of their identity or qualities. These pronouns can select a group as a whole, or select all members of the group individually. They are used in affirmative and negative statements as well as questions and can function as subjects and verb complements. Here is a list of these pronouns:

'All' and 'each' are both classified as universal distributive pronouns. 'All' refers to the total number of people or things considered as a group, whereas 'each' implies that all members of a group are considered individually, even if they are thought of collectively.

'Everyone' and 'everybody' are used to refer to all individuals in a group. 'Everyone' is generally considered more formal than 'everybody,' and is more commonly used in written language.

'Everything' is used to refer collectively to all members of a complete group of something, rather than referring to them individually.

Negative indefinite pronouns refer to the absence of people, things, or places, and include no particular item. These pronouns are negative markers, which means they make the entire sentence negative and the verb remains affirmative. Negative indefinite pronouns can function as subjects and verb complements. Here is a list of these pronouns:

'No one' and 'nobody' both refer to the absence of people. 'Nobody' is slightly less formal than 'no one.'

'Nothing' means no + thing. It refers to the absence of objects. Keep in mind not to use 'nothing' with another negative word such as 'not.'

Alternative indefinite pronouns refer to an item that is different from a previously mentioned one. They typically indicate the second of two people or things, which is different from the one that has already been mentioned or selected. These are versatile forms that can be used in affirmative and negative statements as well as questions and can function as both subjects and verb complements.

'Others' is a plural alternative indefinite pronoun. It can be used to refer to both people and things.

We can use 'the other' as a pronoun, especially to introduce an alternative to something or someone that has already been mentioned in the sentence.

When the indefinite article 'an' is used before 'other', it is written as one word: 'another'. 'Another' refers to an alternative or different thing or person.

Typically, a plural pronoun is used to refer back to indefinite pronouns. Look at the examples:

Most indefinite pronouns are always followed by a singular verb even if they refer to a number of people/things.

Normally pronouns cannot take -'s to form possessive forms. However, indefinite pronouns can take -'s to form a possessive structure:

There are different ways of changing a positive sentence to a negative sentence using an indefinite pronoun:

In this case, the best way is to use a negative indefinite pronoun that corresponds to what the subjects is referring to, whether it is a thing or a person. Take a look at these example:

In this case you can either use a negative indefinite pronoun in a positive sentence or a non-assertive pronoun in a negative sentence. Both of these structures are correct and have the same meaning. Take a look at the examples:

Using indefinite pronouns in negative sentences can be a bit tricky. Not all indefinite pronouns can be used in a negative sentence. The table below summarizes usage of indefinite pronouns in negative sentences.

As you can see, negative indefinite pronouns are negative markers themselves, which means they cannot be used in a sentence that is already negative.