transistors
tiny current magicians. BJTs and MOSFETs switch or amplify—most hobby use is switching.
low-side switch (BJT/MOSFET)
caution
pick a logic-level N-MOSFET with low RDS(on) at your gate voltage. add 100 kΩ pulldown and 100 Ω in series with gate. fact
for BJTs, overdrive the base for switching; use β≈10 as a safe design target.