(shifter linkages aka) Shifter cables run from you shifter to your transmission which would be located somewhere on the top of the transmission usually. You can't miss them. Should be two cables going to some "clutch arms" (my term). Those are what switch the gears in your transmission. Now if you have somebody with you, look at those arms, have them push the clutch down and go through the gears (car off). See if the arms move, if they don't then the shifter cables may have not been put back unto the bracket located somewhere on the transmission. The cables should not have little to no play if they were put back correctly.

Hope that describes it.