Does the distance from the sun cause Earth's seasons?
The distance of the Earth from the sun does have an effect on the planet, but it isn't the primary cause of the seasons. For one thing, we know the Earth is closest to the sun in January, and farthest in July. If this was the only thing that determined the seasons, then we would expect July to be our "winter" and January to be our summer, but this isn't the case if you live in the northern hemisphere.
The real cause of the seasons is the fact that Earth is tilted on an axis. This means certain parts of the Earth are oriented toward or away from the sun for extended periods at different times of the year. As an extreme example, you can imagine the Earth rotating on its "side" so the axis points toward the sun; this would cause an entire hemisphere to be in permanent night, and permanent winter, until the planet travelled far enough around in its orbit to reveal the other side of the planet to the sun again.
On the other hand, if the Earth had no axial tilt, there would probably be no seasons then, either, because the difference between the total amount of energy the Earth receives when it is closest to the sun and farthest away is virtually the same.