How to control the temperature of heating element
Practically you have two main choices involving i) on/off control; ii) average control.

i) Hysteretic control turns the heater on at a lower limit and turns it off at an upper limit. (i.e. on/off).

ii) Drive the heater with a fast switching PWM signal (via Switches and a switch-driver) so that the average value of the temperature is your desired setpoint value. This usually involves feedback and a controller such as a PID.