It walks you through a) systems design of various companies you've heard of; b) how to design common things like a URL shortener or a rate limiter; c) more general topics like you mentioned.
There are also several example chapters available as a free preview, including the module on Instagram.
It's very useful for preparing for interviews that ask, "How would you recreate dropbox?" or "how would you recreate instagram." You know... system design interviews.
I think it's well worth a purchase, only if you can afford it. I feel like the other resources people posted in the thread are better but if you need structured content it's very well done.