Use Sainsmart SSR to control AC outlet with Arduino?
The Amazon Item page Reviews are incredibly helpful for these items, not just the 16 channel, but the 8 and 4 and 2 channel ones by the same manufacturer. Some even have videos. They have it all figured out. The Item page also has the PCB layout and schematic available, though it's not as clear as it could be. You might want to look at some of the reviews for the other versions as well just to get a hang of them.

The J2, 2x10 header is for connection from your Arduino. Pins 1 and 2 are 5 V out (You could power your arduino off the 5 V out), pins 2-18 are Relay 1-16 control, and Pins 19 and 20 are Ground. Logic level Low turns the relay on. Current is about 0.3 mA to 3 mA per channel. Logic Level High is 5 V, so make sure you have 5 V tolerant outputs on your Arduino.

The 16 Channel board takes 12 V, and I'd recommend 1 A just to be on the safe side. From a review:


  * Input Power (12 VDC input)*
  
  
  About 8 mA is required with all relays off.
  Each relay requires about 30 mA when on.
  So max supply current is 8 mA + (16 x 30 mA) = 488 mA (actual measured was 500 mA)
  Because one may use the board's +5 VDC output (2 pins) to power an Arduino/PIC circuit, use a 12V power supply that can provide MORE than
  500mA (depending on your circuit's requirements).
  Note that the switching regulator on the Relay Board should somewhat efficiently (say 70%?) convert the board's 5V power usage to 12 V
  power input requirements. For example: 200mA at +5VDC (1 Watt) does
  NOT mean the +12V supply needs to supply an additional 200 mA also.
  This is because 1 W of power from the +12V supply only requires about
  83 mA ( 12 V x 83 mA = 1 W ); however at say 70% efficiency of the 5 V
  regulator, this goes up to about 120 mA (83 mA / 0.7) but NOT the full
  200 mA.
  
  
  
    NOTE: The best way to discover what 12 V supply is needed (its max current rating) is to ACTUALLY MEASURE the 12 V input current while
    using a "test supply" that can more than handle worst case (with all
    relays ON) then buy the supply that meets your needs. Always use a
    modern "switching" supply (wall wart) because they are smaller, way
    more efficient, generate little heat, and normally use much less
    "vampire power".
  


This is an AC relay board, so you could kill yourself if you mess something up.