CSS Grid Layout allows for two-dimensional page layouts using rows and columns to position elements. It offers several methods for defining the grid including explicit definition with grid-template-columns/rows, implicit definition by letting grid create tracks automatically, and using fractional units and repeat functions for flexible layouts. Elements can then be placed on the grid using line-based positioning with grid-column/row or named grid areas. Media queries allow the grid definition and element placement to adapt at different breakpoints.