Final clauses introduced with um ... zu
Final clauses are dependent on a superordinate clause which usually describe an action.
Action: Wir kaufen einen Saugroboter.
The final clause states the purpose or goal of the action or thing being described. It is separated from the superordinate clause by a comma.
Wir kaufen einen Saugroboter, um Zeit zu sparen.
A final subordinate clause with um … zu is introduced with the conjunction um. The verb of the final clause comes at the end of the sentence. We use the infinitive form of the verb (+ zu). The verb is not conjugated. If the verb is separable, zu is added after the verb prefix.
Ich brauche eine große Tasche, um die leeren Flaschen wegzubringen.
The final clause with um … zu does not have its own subject. Therefore, this sentence structure is only possible if the subject is the superordinate clause and the final clause is the same.
Ich hole einen Besen. Ich kehre die Terrasse.
Ich hole einen Besen, um die Terrasse zu kehren.
If the subject is not identical, you can use a final subordinate clause introduced with the conjunction damit.
Grammatical terms in German:der Infinitiv: The infinitive is the basic form of a verb that is not conjugated. This is the verb form normally found in vocabulary lists or dictionaries. German verbs in the infinitive generally end in -(e)n.