There are three Milankovitch cycles:
Eccentricity is a dimensionless quantity that measures the amount that an orbit is elliptical. Where 0 would be a perfect circle.
The eccentricity of Earth is not static. In a cycle that repeats every 100,000 years, the eccentricity increases and decreases within the range of 0.0034(almost circular) and 0.058(slightly elliptical).
This effects the length of seasons. It also effects the distance that the earth is from the sun during its closest approach and furthest point. When at its most circular, there is 6-7% more solar radiation hitting the Earth at its closest approach. Whereas when the eccentricity is the highest, it is 23%.
Currently, the Earths eccentricity is near its smallest and is slowly decreasing.
Obliquity is the tilt of the rotational axis. This tilt is measured by taking the angle between the rotational axis and a line perpendicular to the orbital plane.
The obliquity is also not static. The obliquity ranges from 22.1 deg to 24.5 deg. This cycle is 41,000 years long.
The greater the obliquity is, the more extreme the seasons are. The winters get colder, and the summers hotter. This promotes the in deglaciation. Higher latitudes receive more sun light then the equator, hence the effect is not uniform.
The lesser the obliquity is, the less extreme the seasons are. The winters get warmer, and the summers colder. This eventually results in the build up of ice sheets. These ice sheets reflect back more sunlight, resulting in even more cooling.
As a result of the gravitational forces from the moon and the sun, the earth wobbles slightly upon its axis. The trend of this wobble relative to the fixed position of the stars.
The precession Earth spans about 26,000 years.