We know that the number of sides of an octagon is 8, meaning it has 8 vertices.

To determine the number of lines that can be drawn from 8 points, note that a line is formed by selecting 2 points. Thus, the number of lines is the number of ways to choose 2 points from 8.

The general formula for choosing r items from n items is:

$nCr = \frac{n!}{(r!(n-r)!)}$

For our case, $n = 8$ and $r = 2$. Applying the formula:

$8C2 = \frac{(8 * 7)}{(2 * 1)} = 28$

So, 28 lines can be drawn from 8 points.

However, the octagon itself already has 8 sides, so we need to subtract these 8 sides from the total number of lines to get the number of diagonals.

Thus, the number of diagonals is:

$28 - 8 = 20$

Therefore, the octagon has 20 diagonals. Hence, the correct answer is 20, which corresponds to option A.

Note: An octagon is a polygon with 8 sides and 8 angles. The diagonals are the lines connecting non-adjacent vertices.