Did they teach Ohm's law? And Kirchoff's voltage law? I hope so. I hope you were taking notes, too
You'll need to apply both laws to each LED in selecting R4 and R5 and you'll need to know the forward voltage drop for your LEDs as well as their max continuous current (usually 20-30mA for the small LEDs).
Do you understand how this circuit works? The 555 alternately grounds the center point between the LEDs (sinking current from the top LED) and supplies voltage (sourcing current for the bottom LED).
This is assuming you want to use LEDs. If you want to use lamps, you'll need to design a circuit that can drive them, by replacing the R4/R5/D1/D2 with the appropriate circuitry (you could use a relay, MOSFET, or BJT) to allow the 555 to source/sink current below it's max ratings yet drive the lamps at the appropriate voltage/current.
As for the components around the 555, there are tons of tutorials on how to set up an astable multivibrator with that IC, and how to select the frequency, although, R3 in that circuit is a potentiometer so frequency is adjustable in the circuit. Up to you to figure out if you need to change anything on the 555 to work at 12V at the frequency you desire.
You *did* go to school to learn electronics, after all
Michael