The way I remember it, based off memory and no looking it up, there was a viking who was exiled from Iceland. Erik the Red, maybe? I think it was Lief Erickson's dad. Anyway, he sailed off and found a chunk of pretty hard land, but sold it as Greenland to get people to sail west.
It probably was a bit less harsh than it is today, because there is some evidence there was a warming trend around the time. But it was still pretty harsh and the settlements didn't last long.
Pretty sure I am off on some facts, but that might be the gist.
edit: I was closer than I thought! Here is the medieval warming period that made it more hospitable: https://en.m.wikipedia.org/wiki/Little_Ice_Age