How to step 12v to 5v and 3.3v
LM78XX is a good option to solve your problem, but I strongly suggest you to investigate on LM2596 and mic29302. These regulators are much better than the old (but always effective) LM78XX series.
If you are new to electronics, I recommend you to start with the newest available components. You will need some additional capacitors for these regulators but it's nothing hard, you will find all required information in the datasheets.
Also, using LM2596 you can adjust the output voltage by changing the resistors values, so you can re-use these components in future projects. LM78XX series has defined output voltages that cant be changed.