Assume the grape vine is a T with two branches running from the top horizontally and there are exactly the same thing about two feet from the top. These are you four branches that produce the grapes. Each branch runs about 4 to 6 feet horizontally. They tentacle by themselves of may have a bit of help with ties. (A wire is run between posts to give the tentacles something to hang on to.)These get trimmed back each year. Takes a bit of skill but there are good diagrams on the internet. The height of the main vertical stem is about six feet.
Now for suckers. They run off the main stem which is vertical or even from the root. These should be cut off, since only one main stem is wanted.
Some people don't prune in the Spring and often end up with a poorly producing vine.
I have four vines and from the Concord in particular obtain a bushel of grapes or around 45 pounds almost every year.