Series vs Parallel

• paralles - current is devided
• series - voltages is devided

Schematcis with breadboard examples

• LEDs in Series - http://www.sysrecon.com/tag/led/

  From the sysrecon.com site:

  Common Resistor values used with LEDs
  3.3 volts to 5 volts: 330ohms
  
  6 volts to 9 volts: 560ohms
  
  12 volts to 15 volts: 1Kohms                                
                              

• LEDs in Parallel - http://www.techdose.com/electronics/Wiring-Multiple-LEDs/226/page3.html

LEDs with 555 Timers

http://circuitdigest.com/electronic-circuits/heart-shaped-serial-led-flasher

http://circuitdigest.com/electronic-circuits/fading-led