Im finishing up an app and writing the help file. I was just going to do a pdf document and display it in a web view.
Is there any standards for help on the iphone i should be aware of, windows has CHM, the html help file format. is there anything similar/comparable for the iphone.
im working in 3.0
Not really - you can just use a folder full of files in standard HTML.
I suggest saurik's "menes" for an iPhone-like UI, but there are many others, such as iWebKit, iUI, etc.
If any part of your app needs explanatory text you should incorporate it into the UI directly, either alongside the relevant UI elements or in popup dialogs that appear the first time you visit that section of your app.
I would very strongly recommend against incorporating a separate help system.
As chpwn suggests, there is no standard help file format, so many applications just use HTML bundled with the application. I do this in my application, and simply use a UIWebView to display the content. I've used a style that fits on the iPhone screen with large text. My users seem to really like the presence of this help.
I've posted the help files online, so you can see the general style and structure I use for them. I simply include them in a separate directory in my application resources using a custom Copy Files build phase.