i want to create a circuit that will be able to drive 3.2v 8w leds that's powered by 12vdc that is controlled by an attiny84 but i don't know what kind of switch to use
A N MOSFET rated at least 5Amps and 25V would be OK.
Does the tiny84 output 5V signal levels.? If yes, the FET should have that low Vgs specification.
Series resistor to drop 5.6V at 2.5A , 2.5R at 10Watts
You can use the FQP30N06L, as I use in this schematic to drive a clock coil. It has a low gate voltage and will turn on between 1 and 2.5 volts, will control about 35 amps and operate with Source to drain voltage up to 60 volts. The 3.3 volt logic levels from my Raspberry pi zero W drives it fine. The LED and limiting resistor is not required, its just to see if the output is active. The gate can be connected directly to the output pin of your device. Joe