This part is short and actually can be skipped.
You may have a super-simple app which is ready for launch immediately after development. For more complicated apps, you would better to share them with Beta testers first. There are some options to consider.
In this case, you need a website or a landing page with cheap hosting for ZIP or DMG archives. For your help, there is a free component named Sparkle which can be used for periodic and automatic client updates. While distributing such Alpha or Beta versions, you would collect user feedback by email.
There is also a great service named Hockey which enables you not only to distribute Beta-builds but also collect crash reports and user feedback. Additionally, you can use this service even after public release to fix the most annoying issues in the future updates.
Once beta testing is done and you are ready to ship 1.0, you need a distribution channel. See you after the weekend.