Saying what you do something for
A purpose clause answers the question Wozu? (what for?). It does not give a cause, as weil does, but a goal you want to reach. German has two structures for it, and you choose by counting the subjects.
Ich lerne, um die Prüfung zu bestehen.
I'm studying to pass the exam.
one subject: I study, I pass
Ich erkläre es dir, damit du die Prüfung bestehst.
I'm explaining it to you so that you pass the exam.
two subjects: I explain, you pass
um … zu: one subject
The um … zu group has no subject and no conjugated verb. It borrows the subject of the main clause. The infinitive stands last, with zu directly in front of it. A comma comes before um.
How the group is built
The group can also come first. Then it fills position one, so the verb of the main clause follows right after the comma.
Ich fahre mit dem Rad, um Geld zu sparen.
I cycle to save money.
Sie ruft beim Arzt an, um einen Termin zu machen.
She's calling the doctor to make an appointment.
Wir fahren früher los, um pünktlich zu sein.
We're leaving earlier to be on time.
Um besser Deutsch zu sprechen, schaue ich Serien auf Deutsch.
To speak German better, I watch series in German.
group first: the verb comes right after the comma
damit: a second subject
Once the goal belongs to somebody else, um … zu has no place for the new subject. damit opens a normal subordinate clause, like weil: it has its own subject, and the conjugated verb comes last.
Two subjects, two clauses
damit is also possible when both halves have the same subject, but um … zu is shorter and is what people normally say. A modal verb belongs in a damit clause, where it goes last: damit du uns finden kannst.
Ich stehe früh auf, damit die Kinder pünktlich in der Schule sind.
I get up early so that the children are at school on time.
Ich schicke dir die Adresse, damit du uns findest.
I'll send you the address so that you can find us.
Er spricht langsam, damit ihn alle verstehen können.
He speaks slowly so that everyone can understand him.
Damit alle mitkommen können, nehmen wir zwei Autos.
So that everyone can come along, we're taking two cars.
clause first: the verb comes right after the comma
