How to copy out a substring using MID(), example uses a FIND() to determine the start and end points. For instance, the example below grabs text that falls in-between [ ]. MID's format is (cell, starting point, ending point), so FIND() is used here to find the starting point of the [ character and the end point of ], which are both nested within the MID() formula, telling Excel to grab the text between [ ] and copy it into the destination cell.
=MID(J2,(FIND("[",J2)+1),((FIND("]",J2)-1-(FIND("[",J2)))))