The star tracker is really just a small equatorial mount.
And in the most basic form, it is really just a motor with fixed (alternatively in sidereal, lunar and solar rates) tracking speeds. The motor turns a mounting plate for a small telescope attachment or a camera ball head mount.

The mount, along the motorized axis, is equipped with a small polar telescope. This has some markings with constellation orientations and a grade scale for how to orient Polaris on the northern hemisphere and the octanes constellation on the southern hemisphere.

Polar align
On the northern hemisphere, polaris can be used for polar alingment. By adjusting the altitude on the mount for the correct latitude and the azimuth to point north, Polaris comes within the field of view in the polar scope.  The position of Polaris is adjusted in the polar scope acording to the location, time and date. Today there are apps to assist with this.

This is called a polar alignment.

The accuracy of this alignment will dictate how long exposure one may have and what focal length you can use before stars stars to form trails in the image.