The paragraph was saying how they came and how many came. They originally landed in Greenland. It was very cold and harsh so they went exploring some more they landed of the east coast of Canadian province Newfoundland. At first the was only about 400 people there but over time there came to be about 2- 4,000 people there. Most of them were raiders and scavengers but others helped them and were blacksmiths and farmers.
It said during the tenth century vikings left their native lands and went exploring somewhere else. They were well documented and many believe they were the first. They were said to be led by Leif Erikson, son of Erik the red, They sailed to a place they called "Vinland" which is now the Canadian province Newfoundland Labrador.
In this paragraph it tells me that the vikings were from Scandinavia, Sweden, Denmark, and Norway. They were basically Pirates they would sail and steal gold and loot. Around 700-1100 AD they left Scandinavia and went to Ireland and the UK. Some gave up on that life and became farmers, black smiths, and ship builders.
This paragraph wad talking about why the vikings left. The reason they left was because of over crowding and there wasn't enough land to sustain the lives of the many people they had so they started taking more land and eventually driving them to go sailing for more land.