Where you have plenty of room to let the grape grow then you may not have to prune too hard for a year or two.
There are many ways to train grapes, but one method that I have found very successful on trellis work is this.
You train the leaders that you wish to use as a frame for your grape along some form of support system.
How many leaders you let your plant have is decided by either the room they can have and also the strength of the vine.
These leaders are left alone as they are just the carriers of the side shoots that will do all the cropping.
They will only be pruned once they have reached the full length that you can let the vine have.
Along the length of these main structure branch/ branches, side shoots will grow out. These are allowed to grow and are tied in to a support wire until they produce a bunch of grares in the early summer. Then they are tipped a couple of leaves beyond the forming bunch so that energy is put into the growing fruit.
Dureing the latter part of the summer you will find that extra growth will occur on these shoots...just cut this off now and then to allow good light to fall on the grapes as they ripen.
In the winter these side shoots are cut back to two to three buds.
( In theory they could be cut back to one bud....but if you then get a spring frost you have no spare buds waiting as replacements. )
This is a reliable way, but as first stated it is only one of many types of training that you can do.
Hope that helps.