Many Zen groups provide instructions for newcomers. If they didn't you should just ask, or maybe it's on their website. Otherwise you can read online and in books.
Here is a good one from the Soto teacher Shohaku Okumura: Zazen instruction
This is a classic teaching by the great Hanshan Deqing: Essentials of Practice and Enlightenment for Beginners
You should also familiarise yourself with Zhiyi's shorter meditation instruction for a more in depth knowledge: The Essentials of Buddhist Meditation
Thanks Astus, this is what I am saying though...in traditions that use stuff like Shamatha and Vipasanna you are directed to use the mind in certain ways, this kind of method seems absent from Zen practice with little talk about directing the mind one way or another. Most of the basic instruction seems to be mudra, posture, but little talk about the mind making any sort of directed effort. Is this pretty much part and parcel of Zen, being "objectless"? Is it antithetical to Zen to actually try to direct the mind, or to "try" at all in that sense, this is the impression I have always had.
It definitely was not intended as a complaint of lack of instruction if it came out that way.
I guess i'm coming at it from the point of view of my own experiences, struggling to understand the relationship between Shamatha, say breath-focused, and Zen type meditation. Is Shikantaza the same as Shamatha without an object, or is it something else entirely? Is it Vipassana without analysis?
I know they are ridiculous questions but they are coming up for me now that I have moved to another tradition, and am trying to reconcile my habits.