Need to add C wire for WIFI stat
Of the two lower screws on the tan panel one is already connected to your thermostat, the other one is he C terminal.  (probably the left one is C)



in a typical extra-low voltage thermostat system a transformer provides 24V AC , one terminal goes to the thermostat and the other terminal (called common or "C" ) goes to the relays and solenoids that control control the equipment,  that shiny thing looks like a 24V doorbell transformer and the tan panel is mounted over the output terminals, so the terminal with most wires is almost certainly "C"