Keyword: control

To begin with, you can use any tethering software -- only later will you use the advantages of solutions tailored to astrophotography. Here I'll discuss both options.

Observing stars becomes easier if you don't have to constantly make adjustments. This is even more important, if you want to make long-exposure photos of the sky. The solution is simple & elegant -- the Earth rotates around it's axis and if you counteract that rotation, you keep looking at the same position in the sky. There are different names for solutions to do that, most notably an "equatorial mount". Barndoor- and other star-tracking accessories all use the same principle and require the same preparation steps -- THE POLAR ALIGNMENT