If you are facing your first iOS project, take a look at the Getting Started tutorial that Apple has published in the iOS Developer Library. You might also find useful to follow one of the many awesome Objective-C tutorials and books available over the Internet. A random pick of a high rated introduction to the language is Learn Objective-C.
For a more in depth explanation of the iOS development science, there is a great Stanford course freely available at iTunes U: iPad and iPhone Application Development.
And remember, the best way to learn is by practicing. So, start coding!