It depends on what state you are in. Generally, it is only informational. The state wants it for some reason and you can't e-file without it. Mostly, it is used, by the state, to allocate revenue to the various school districts. Some states actually have a School District (SD) Income Tax (SDIT). If your state does, that will come up later in the state interview. Not all school districts have an income tax.
If you are in Ohio, be aware that TurboTax (TT) does not automatically prepare a School District return (form SD100), you must initiate it.
At the screen, in the Ohio program, titled "A few things before we wrap up your state taxes"
scroll down to School District taxes.
Or later at the screen "Your 2023 Ohio Taxes are ready for us to check"
-Click Other situations
-Scroll down to School District taxes.
Usually the School District Income Tax (SDIT) return is e-filed with the state return, but there are exceptions. Read the Ohio 'filing instructions" that TurboTax prepares, They will tell you if the SD100 was e-filed or if you have to mail it.