If you have not already done so, create a new Xcode project from one of the templates. Go through the code and pick out the Objective-C constructs that have been discussed in this hour. Be certain to run the code! Only hands-on experience with the code will help you understand what the code is doing.
Explore one or more of the sample code projects on developer.apple.com (these are often more complex than the Xcode projects). You might want to search for specific features, such as protocols or delegates, that you want to explore.