This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
thanks for your question. Especially the first chapters build on one another and you should read them in order. Some of the later chapters (about GCD, Core Data or error handling, for example) can also be read on their own and just expect you to have fundamental Obj-C knowledge that you will have gathered in the first chapters.