As a new iPhone developer myself, I've found apple's sdk documentation to be the best for learning. The iPhoneCoreDataRecipes package has been my go to for figuring things out. It's got a little bit of everything in it.
I tried to do web tutorials - there are a ton out there, just search iPhone tutorial on the web or on SO - but I found most of them lacking.
There are a couple of classes that you can you use to retrieve a web request. NSURLConnection will be the best one for making POST requests, and if you're querying restful services initializing an NSString with a URL is the easiest method.