Afraid

1. In informal English, we use afraid (of) much more often than fear. 

Don't be afraid. 

Are you afraid of the dark?

     Do you fear the dark? is possible but would probably not be used in conversation. 

2. I'm afraid often means I'm sorry but... It is used to introduce apologetic refusals, bad news, etc. 

I'm afraid I can't help you. 

I'm afraid your wife's had an accident. 

    I'm afraid not and I'm afraid so are often used in answers. 

'Can you lend me a pound?' - 'I'm afraid not.'

'It's going to rain.' - 'Yes, I'm afraid so.' 

3. Afraid is one of the adjectives that cannot normally be used before nouns (in 'attributive' position). Compare the following: 

John's afraid. 

John's a frightened man (Not: ...an afraid man). 

    We do not usually use very before afraid; instead, we can say very much (especially when I'm afraid means 'I'm sorry'). 

I'm very much afraid he's out. 

    *Learn later about other adjectives like this and gerund and infinitive structure with afraid.