Look at this dialogue:

• A: What’s this machine for?
• B: It’s for cutting

The question What is it for? asks about the purpose of something (what we use something for). When we describe the purpose of a thing, we use for + –ing. Here are some more examples:

• This is an instrument for measuring wind speed.
• This tool is used for making

Now look at this dialogue:

• A: What does he need my camera for? (= Why does he need my camera?)
• B: He needs it for his work. (= His work is the reason why he needs the camera.)

The question What … for? asks about purpose. To talk about someone’s purpose, we can use for + noun. Here are some more examples:

• A: What did he go to the shops for?
• B: He went for some bread. (= He wanted to buy some bread.)

• I read the BBC News website for the articles on British politics. (= … in order to read the articles on British politics.)

Now look at this dialogue:

• A: What does he need my camera for?
• B: He needs it to take some photos. (= … in order to take some photos.)

To talk about someone’s purpose, we can also use to + infinitive (e.g. to take). Here are some more examples:

• He went to the shop to buy some bread. (= … in order to buy some bread.)

• John phoned the police to tell them about the burglar.