If something is for someone, they are intended to have it or benefit from it.
He left a note for her on the table.
She held out the flowers and said, ‘They’re for you.'
I am doing everything I can for you.
You use for in front of a noun phrase or -ing form when you state the purpose of an object, action, or activity.
Some planes are for internal use, others for international flights.
The mug had been used for mixing flour and water.
You use for in front of a noun phrase when you are saying why someone does something.
We stopped for lunch by the roadside.
I went to the store for a newspaper.
Don't use ‘for’ with an -ing form when you saying why someone does something. Don't say, for example, ‘He went to the city for finding work’. You say ‘He went to the city to find work’ or ‘He went to the city in order to find work’.
People would stroll down the path to admire the garden.
He had to hurry in order to reach the next place on his schedule.
You use for to say how long something lasts or continues.
I'm staying with Bob for a few days.
You also use for to say how long something has been the case.
I have known you for a long time.
He has been missing for three weeks.
When you use for to say how long something has been the case, you must use a perfect form. Don't say, for example, ‘I am living here for five years’. You must say ‘I have lived here for five years’.
Don't confuse for with since. You use since to say that something has been the case from a particular time in the past until now.
Exam results have improved rapidly since 1999.
I've known her since she was twelve.
used to mean ‘because’
In stories, for is sometimes used to mean ‘because’. This use is rather old-fashioned, and is not used in conversation.
This is where he spent his free time, for he had nowhere else to go.