In German, this sentence must be broken down into a main clause and a subordinate clause. Er hat uns den Film erlaubt zu sehen. See page 242 for an explanation of this problem. Vorigen Sommer lernte ich zu segeln. This verb usually functions like a modal auxiliary, i.e. the second verb is not preceded by zu .
Exceptions occur only when the sentence is fairly long and complicated.
Ich war so berrascht, da ich nicht wu te, was zu sagen. In German this must be stated as a subordinate clause.