What do these symbols indicate on the ATC display?
The white squares are aircraft - it's course is indicated by a line. Then there is a datablock showing Callsign "FWA170C", its altitude F053 = Flighlevel 53 = 5300ft, climbing to an assigned flightlevel 190 = 19000ft.
A = altitude - below a defined transition level
F = flightlevel (steps of 100ft) - above a defined transition altitude

Transition altitude and level depend on the location and weather.

Then you have the airports, navaids, nav-fixes and the control zones showing.