für
for
Indicates the recipient or beneficiary of an action or thing; expresses a purpose.
Ich habe ein Geschenk für dich gekauft.
I bought a gift for you.

for
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for
Indicates the recipient or beneficiary of an action or thing; expresses a purpose.
Ich habe ein Geschenk für dich gekauft.
I bought a gift for you.

The preposition 'für' always requires the accusative. Make sure to decline the article and pronoun after 'für' correctly.
Diese Blumen sind für meine Mutter.
These flowers are for my mother.
In addition to a recipient, 'für' can also express a purpose or goal. It then answers the question 'Wofür?' (for what?) or 'Zu welchem Zweck?' (for what purpose?). In this case, it is often followed by an abstract noun.
Wir lernen für die Prüfung.
We're studying for the exam.
When 'für' indicates a duration of time, it describes the planned length of a future or present event. Typical combinations are 'für einen Tag' (for one day), 'für ein paar Stunden' (for a few hours), or 'für immer' (forever).
Ich bin für drei Tage auf Geschäftsreise.
I'm on a business trip for three days.
The phrase 'für etwas sein' (to be for something) is very common for expressing agreement. It is often used in contrast to 'gegen etwas sein' (to be against something).
Bist du für oder gegen die neue Regelung?
Are you for or against the new regulation?
In this meaning, 'für' introduces a comparison. The structure is often: 'Für [Bezugsgröße] ist/hat [Subjekt] ...' (For [reference point], [subject] is/has ...). This puts a statement in relation to an expectation.
Für sein Alter ist er schon sehr reif.
For his age, he is already very mature.
When 'für' means 'anstelle von' (instead of), it is often used with verbs like 'sprechen' (to speak), 'antworten' (to answer), or 'einspringen' (to step in) to express representation or substitution.
Der Anwalt spricht für seinen Mandanten.
The lawyer speaks for his client.
to / too / closed
'zu' and 'für' can both have to do with purpose or aim, but they appear in different structures. 'zu' often comes before an infinitive, for example in 'Zeit haben, etwas zu machen' (to have time to do something) or 'um etwas zu lernen' (in order to learn something). 'für' comes before a noun or pronoun and often names the recipient, the benefit, or the purpose of something. Learners confuse the words because both can express a kind of purpose. Pay attention to the form that follows: an infinitive verb with 'zu', a noun or person with 'für'.

Diese Tasche ist für meine Schwester.
This bag is for my sister.
Ich habe heute keine Zeit, den Antrag auszufüllen.
I don't have time today to fill out the application.