Every 11 years the Sun's magnetic field completely flips, meaning its north and south poles switch places. The solar cycle affects activity on the surface of the Sun, increasing the number of sunspots (which are caused by the Sun's magnetic fields) during stronger (2001) phases than weaker (1996/2006) ones.
One way to track the solar cycle is by counting the number of sunspots. The beginning of a solar cycle is a solar minimum, or when the Sun has the least sunspots. Over time, solar activity - and the number of sunspots - increases.
The middle of the solar cycle is the solar maximum, or when the Sun has the most sunspots. As the cycle ends, it fades back to the solar minimum and then a new cycle begins.
Giant eruptions on the Sun, such as solar flares and coronal mass ejections CMEs), also increase during the solar cycle. These eruptions send powerful bursts of energy and material into space that can have effects on Earth. For example, eruptions can cause lights in the sky, called aurora, or impact radio communications and electricity grids on Earth.
Credit for image above: https://www.dailymail.co.uk/sciencetech/article-6649689/A-year-sun-Animation-reveals-deathly-quiet-2018-solar-minimum-approaches.html