Answer:
A) fill the grid with 20 rectangles of the exact same size and rotation
B) place a rectangle so that there is an exactly 1 tile gap between the edge of the grid and the edge of the rectangle
Explanation:
The question is asking you to place the shape you have been given onto the grid over and over with no overlaps, until you either fill the grid or mess up and find that you cannot. In mathematics, this is called tessellation.
In A), a way to fill the grid completely is to place the rectangles in an orderly, grid-like fashion. You should draw 19 more rectangles onto the grid so that there are 20 total in a 4x5 grid of rectangles.
In B), the question is telling you to intentionally mess up so that filling the grid is impossible. Placing a rectangle awkwardly in most places will achieve this, not just doing what I suggested in the answer. The important thing is that the placement will block the placement of another rectangle, making filling the grid impossible.