Sentence:
先生、こちらは学校の友達のJennyです。
This sentence is an example of の's ability to convey a hierarchy of information, but I still don't get how you would know where to put the two のs. How do you use の in this sentence?
Japanese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Japanese language. It only takes a minute to sign up.
Sign up to join this communityの can represent two different types of relationship.
In your example, "学校の友達" describes the former type of relationship (i.e., 友達 belonging to the 学校), and "友達のJenny" describes the latter type of relationship (i.e., "My friend Jenny"). You have to get used to it.
(BTW, 'of' in English is similar; compare "The city of London" and "A city of UK".)
See this question for details: What's the difference between 日本人の学生 and 日本の学生 ?