Read, read, read. Find a nice simple project and give it a try.
Learn about...
MOSFETs, they're used for switches in our lights. Either high speed switching used in step up or step down regulators for LEDs. Low speed switching used when you just use a big MOSFET in place of a high current switch in a powerfull incan.
Linear regulators or Low Drop Out regulators (LDO). These are self variable resistors that adjust their resistance to maintain a constant output voltage or current.
PWM or Switched Mode Power Supplies. These are the controllers used to build step up or stepdown drivers for LEDs. Or a PWM regulator for powerful incans like the PIR.
For PWM/Switched mode supplies requires an oscilloscope.