Earth has two types of motion, one is called revolution around Sun and the other rotation on its axis. The revolution around Sun in its orbit causes seasons to happen and the rotation on its axis causes day and night to happen. The length of day & night depends on your location on earth, the time of year and the tilt of earth on which it is rotating.
Length of days/night
Day duration is typically of 24 hours. Since day and night are not of the same length. Days are shorter in winter than summer. The tilt towards sun makes the daylight and night time different. As earth is 23.5 degree tilted, if the Northern hemisphere is tilted towards sun the days on the pole gets longer hence summer starts in that part. While winter on the southern hemisphere.
Solstice and Equinox
Seasons start from solstice and equinox. Therefore solstice and equinox are important solar terms in a year. They have been celebrated from ancient time, because day and night duration gets changed and the rising position of sun in the sky starts changing its position. Day and night duration gets equal on equinox i.e spring or autumnal equinox. While the longest day of the year happens on Summer Solstice, and the shortest day happens on winter equinox. Summer solstice 2020 in northern hemisphere is going to take place on June 20 this year.
Position on Earth
Your location on earth also is an important factor for defining day/night duration. On Equator the day and night duration is almost equal throughout the year. A small change of duration occurs but when you move towards pole from equator the difference is most obvious. When you arrive on the arctic the day duration is the most in summer and the day duration is the least in winter.