Something, anything, everything, nothing etc: further information

These have the same meaning but 'not' + anyone, anybody, anything and anywhere are more commonly used. No one, nobody, nothing and nowhere are considered more emphatic:

Although the pronouns take singular verbs, we sometimes use 'they', 'them', 'their' and 'theirs' rather than 'he', 'she', 'him', 'her', 'his', and 'hers' with those relating to people. For example:

Someone gave me their ticket so I can go to the concert.

If anyone understands this, can they explain it to me, please?

Everyone needs to understand their responsibilities.

No one has finished writing theirs yet.

We often do this when we don't want to specify a gender. It is much better than using 'he or she' or 's/he', for example.

'Not anyone' etc. isn't usually used at the beginning of a sentence or clause:

Not anyone has to work at weekends.

Not anything was provided. 

We looked for a hotel but not anywhere in the city was suitable.  

Instead, we use no one or nothing or nowhere:

No one has to work at weekends.

Nothing was provided.

We looked for a hotel but nowhere in the city was suitable.

However, we can use 'not everyone'.

Not everyone is happy about the new rules.

I tried to explain that not everything about this job is easy.

The pronouns beginning with 'any' can be used in affirmative sentences which include a word with a negative or restrictive meaning:

We rarely invite anyone here in the winter - the roads are too dangerous.

It's unlikely that we'll receive anything before the end of the week.

We failed to find anywhere that was suitable for the conference.

We also use it in clauses beginning with 'before': 

Let's deal with it now before anyone complains.

Before buying anything for the new office, we should decide exactly what we need.

See also 'hardly' in 'Intensifiers'.

We do not usually use someone etc. in negative sentences:

I don't know someone there. 

I don't know anyone there.  

I know no one there.            

However, it is possible if, for example, the person is unknown or we avoid naming the person or we are being ironic:

     Someone didn't remember to lock the door last night.

Or with 'something':

Something isn't right here.

I didn't do something wrong.

We use intensifiers to give extra information. Here are some examples:

   Have you seen my keys? I can't find them anywhere.

   Not everybody takes a suitcase with them on the plane - some people just have hand luggage. 

    There's absolutely nowhere I'd rather be right now!  

For more information, see some, any, no and every.