Hi Iane,

When do I use other and when do I need to use another in a sentence?

Other is used for something or someone different.

For example: The other people in the room are loud, but you are quiet.

Another is used when you talk about one more person or one more of something

For example:  I finished my oral English exam, but I have another English exam tomorrow.

The word 'another' is just 'an' and 'other' written as one word. It's used for singular, countable nouns.

The book - the other book

My book - my other book

A book - a other book   an other book    another book

That's all it is.

An + other = another. 

Simple, isn't it?

Hi Lane!

Here's another example for you which has a slightly different meaning. It's a collocation really:

They helped one another.

'One another', in this example, means 'each other'. It emphasizes the similarity NOT the distinct/unique qualities of the individuals involved. It is each person who helped the other person and each one who was helped by the other one. 'So the words 'One another' tell about a common relationship shared by people/things/entities/qualities.

In the example I've given it is implied that 2 people helped each other. If you wanted to use 'one another' to talk about 3 or more people who helped each other you would simply add the word 'all'.

e.g. They all helped one another.

However, in this example the extent of the help is not clear. It does not necessarily mean that each person helped every other person (although it could mean that) but simply that each person did help someone. This example states a general fact that applies to the whole group. They all had one thing in common -- they all 'helped' at least one other person.

I hope this is helpful,

Thomas

e.g. 

I have 2 brothers, one is taller, the other is slimmer. (only two)

I understood now. Thank you!