Furnace blower comes on first to purge combustion chamber.........then sail switch & hi limit switch make up allowing dc power to circuit board for gas valve & ignitor. The clicking you hear is the ignitor.
So.......
Main flame is not lighting off. Either because ignitor is not correctly positioned over burner slot, main gas burner dirty (slots blocked by rust/debris/mud dabber nests etc.), low propane pressure, gas valve not opening
Probably needs a good cleaning.......connection/contacts on circuit board, main burner assembly, main burner orifice, combustion chamber and make sure nothing is blocking return air to furnace.