This document summarizes a unit from the book "Grammar in Use" about the usage of "to", "for", and "so that". It explains that "to" is used with an infinitive to indicate purpose or reason. It distinguishes between the adverbial and adjectival uses of "to". It also explains that "for" is used with a noun or gerund, while "to" is used with a verb. Finally, it notes that "so that" is used to indicate purpose, especially with negative purposes or when used with modal verbs like "can" and "could".