For

For is usually a preposition and sometimes a conjunction.

For: purpose

We use for to talk about a purpose or a reason for something:

In questions we often use what … for instead of why to ask about the reason or purpose of something especially in informal situations:

We often use for to introduce the person or people receiving something:

She bought a teapot for her sister.
Mike Cranham and his staff at the hotel cook for 800 people a day, on average.

We use for with a period of time to refer to duration (how long something lasts):

There’s a lovely open-air pool near us. We usually go there for a couple of hours in the evenings when it’s warm enough.

warning

Don’t confuse for and in when referring to time:

We’re going to Cape Town for two months. (We will spend two months in Cape Town.)
We’re going to Cape Town in two months. (We’re leaving to go to Cape Town two months from now.)

After a negative we can use for and in with the same meaning. In is particularly common in American English:

We use for to refer to an exchange:

[sign in a food shop]
2 for £2 or £1.36 each. (Two for two pounds or one pound thirty-six each.)
I got 124 euros for 100 pounds at today’s exchange rate.

We sometimes use for as a conjunction meaning ‘because’. We use it in very formal, and often literary, contexts:

Chasing the white stag through the forests, never catching it, of course, for it is a creature of legend.

We often combine for with a verb to form a multi-word verb:

You will find other multi-word verbs with for in a good learner’s dictionary.