Complex sentence: Stary Oskol serves as the administrative center of Starooskolsky District; however, it is not administratively a part of it and is incorporated separately as a town of oblast significance--an administrative unit with a status equal to that of the districts.
Split into simpler sentences: Stary Oskol serves as the administrative center of Starooskolsky District, although it is not administratively a part of it. Administratively, it is incorporated separately as a town of oblast significance--an administrative unit with a status equal to that of the districts.