This "shikantaza," just sitting. I gather from my readings that it is a more advanced form of zazen. Something not for beginners. Beginners can start with breath counting or just breath awareness (as Thich Nhat Hanh teaches).

How do you "Just Sit" or "Only Sit"? Where do I put my attention?

Here is an interesting link that I found to help me answer this question:

www.angelfire.com/electronic/awakening101/shikantaza.html