This circuit can be used to switch a low voltage (12V) AC load with an Arduino or other microcontroller. A positive signal on the entrance will bring T1 into conduction, triggering the Triac via emitter resistor R2. D1 and C1 are just there to provide DC-power to the transistor. R3 will pull the base low. The circuit will work without R3 but it might react erratic: during start up of your nicrocontroller, the pin connected to the circuit might be undefined and switch someting while it is not desired. Also, as negative impulses can trigger a TRIAC, switching from high to low can trigger the triac if R3 is not present.
The Triac should be cooled with a metal profile. remember that the Gate is galvanically connected with the metal housing of the Triac.
WARNING: This is for LOW AC voltage only. Switching a high voltage AC requires use of opto couplers to isolate the High Voltage from the microcontroller.
Notes. I have used an SC141B Triac rather than a TIC206 as I had that around and it is 110 V. max. In a 220 V. country I am not likely going to use that soon for another project. The picture of the mounted PCB does not show the heatsink yet. It is advisable to use a heatsink. The printdesign can be downloaded here. There is space for various size capacitors. Mine seems very big but it is a very old one I still had lying around. You may want to move the position of D1 to make it a bit easier to mount a heatsink. The Diode D1 does not really need to be a 1N4007. The DC part of the circuit does not really need much power. a 1n4148 would be OK, but they have the same price and I had a 1n4007 lying around.
The circuit can be simplified by just using a pin of the arduino to trigger the triac via a resistor. That will probably work for a TIC206 that needs only 5 mA, but other Triacs may need a bit more than is advisable for your arduino.