Earth's axial tilt is responsible for the four seasons that occur during the year. When a hemisphere is tilted towards the sun, that region receives more sunlight and becomes warmer, while the hemisphere that is tilted away receives less solar energy and is cooler.
Earth's axial tilt stays effectively constant throughout the year. This means that for three months, the North Pole is tilted towards the sun, and for three months it is tilted away. For the remaining six months, the tilt is at a perpendicular angle to the sun, causing no significant difference in the amount of solar energy reaching each hemisphere.
In addition to the seasons, Earth's axial tilt affects how many hours of sunlight a given region enjoys. For instance, when the North Pole is tilted towards the sun, the extreme northern reaches of the planet are in sunlight for most, if not all, of the 24-hour rotational period. When it is tilted away, Earth's own surface begins to block the sun's rays, resulting in longer periods of darkness. This effect is magnified the further north or south an observer is located, and is negligible near the equator.
Earth's tilted axis also affects how constellations and other heavenly bodies appear to move through the sky. This is why during some parts of the year, stars and planets may appear directly overhead, while at other times they seem to barely rise above the horizon.