Since Zen Buddhism is primarily a practice tradition, you can easily learn Zen practice online.
However, eventually you’ll need to establish a relationship with a Zen teacher. Without such a relationship, your practice will never mature.
Here’s a great video that will teach you how to do Zen meditation practice. It’s very clear and complete:http://www.youtube.com/watch?v=csyCrcpDs…
Here are additional meditation instructions:http://www.mro.org/zmm/teachings/meditat…
Here are collections of teachings (print and audio files) that can support you in your practice:http://www.sfzc.org/zc/display.asp?catid…http://www.mro.org/zmm/teachings/discour…
If you have any questions, feel welcome to write to me.
Best wishes on your path!

Related Reading:

Questions to a Zen Master: Practical and Spiritual Answers from the Great Japanese Master