No problem very valid question.
Best route is to take M2 i.e. motorway from Islamabad to Lahore. When you reach Slaim chowk you will see signs for Sargodha turning. Take directions from those signs and get off from motorway. The raod is good and you will reach Sargodha from Pindi in about 4 hours.
If you do not want to take motor way then get on GT road abd turn from sarai Alam Gir (Near Jehlum) to Mandi Bahaudin, Head rasul and follow signs to Sargodha. It will take 5 to6 hours by car and raod is just so so. Quite bumpy at some places.
Third route which is more adventurous is to take GT road and then turn to Chakwal. From Chakwal go to Kallar Kahar and follow signs to Srgodha. Total time is 6 hours. Hilly, winding and narrow roads. Route not recommended as it is tiring.
Best route is Motorway through Salim to Sargodha.
Enjoy your travel.