Area is the amount of space a flat shape covers, measured in square units. By counting the unit squares that fit inside a shape, you find its area. Rectangular areas can also be found by multiplying length times width.
Use graph paper or tiles to cover shapes. Count the squares inside. For rectangles, show how multiplying the number of rows by the number of columns gives the same answer as counting.
You already know how to count squares inside a shape — that counting process is exactly what area means. Area is the answer to the question: "How many equal-sized squares fit perfectly inside this shape, with no gaps and no overlaps?" Each of those squares is called a unit square, and the area tells you how many of them it takes to cover the shape completely.
Think about a shape drawn on graph paper. Every small square on the grid is one unit square. If you can count 12 squares inside a rectangle, the area is 12 square units. This is concrete and direct — you are literally counting the covering. The unit square is the measuring tile, just like inches are the measuring unit for length.
Here is where your work with arrays connects. You have seen that an array of 3 rows and 4 columns has 3 × 4 = 12 dots. A rectangle that is 3 squares tall and 4 squares wide has exactly 3 × 4 = 12 unit squares inside it. The rows and columns of the rectangle are the same structure as the array. So instead of counting every square one by one, you can multiply length × width and get the same answer. For a 5-by-6 rectangle, instead of counting 30 squares, you multiply: 5 × 6 = 30.
This is why area and multiplication grow up together. For now, both approaches — counting squares and multiplying — give the same result, and seeing that they match is the key insight. Later you will use the multiplication shortcut for bigger shapes, but the meaning is always rooted in counting unit squares.