Some of those relationships are direct, and some are not. This row represents all the people on the chart who are members of your generation. Move up one row, and you're looking at your parent's generation. Down one row and you're looking at your children's. In other words, they've descended the same number of steps from the shared ancestors.
Siblings share a set of parents.
1st cousins share a set of grandparents. 2d cousins share a set of great grandparents. They are not in the same generation as you. Now your 1st Cousin's children and your children are in the same generation again, but the shared ancestors are their great grandparents. That means that they are full 2d cousins.