First, have you gone through Apples docs on submission: http://developer.apple.com/iphone/appstore/submission.html
In general, the process is to log into itunesconnect.apple.com using your iPhone developer account, click "manage applications", then "Add new application" and fill in the forms.
You need to build a distribution version of your app codesigned with an iPhone Distribution cert. The Distribution cert can be obtained from the iPhone Developer Portal (http://developer.apple.com/iphone click "iPhone Provisioning Portal" on the right.) When you have a distribution build, you just need to zip up the app. Open the MyAppProject/build/Release-iphoneos directory in Finder, right-click on myApp.app and select "Compress 'myApp.app'" from the context menu. For very large apps, you will need the Application Loader available from the App Management section of iTunesConnect to upload the binary.
In general, it takes at least a week for an app to be processed by Apple. Typically, as soon as Apple accepts the app, it's available for sale. That said, if you don't tell anyone about the app, no one will find it.
For me, the hardest parts of the app submission process are writing the blurb and coming up with the list of keywords.