If you use one of my sketches, they are all set up to use the Arduino’s internal pull-up resistor. This means that each digital pin used by the sketch as a “contact sensor” will have 5 volts on it by default. When you connect the digital input pin to the Arduino Ground pin, the sensor will register as “closed” - meaning the door or window is closed. When the connection is broken, the door or window will register as “open”. So the wiring through the switches you purchased is very simple. Just connect one lead from every sensor to a common GND pin on the arduino (I use a small breadboard to make this easy to change as necessary) and the other lead from each sensor connects to a corresponding digital input pin on the arduino based on what pins you choose within the arduino sketch.
If all you want is to monitor doors and windows, take a look at my ST_Anything_Doors_Windows.ino example in my github repository. If you want to add some of the other capabilities that I have implemented, like temperature/humidity, luminance, motion, etc…, take a look at my ST_Anything.ino example.
Note, pay close attention on how to wire up the Arduino to the ThingShield if you decide to use an Arduino MEGA 2560 (recommended if you have a large number of sensors you want to use.) Using my ThingShield library with the MEGA, you’ll need to add jumpers between pins 2 and 14, and pins 3 and 15.
One thing you will need to understand (and I am glad you’re a software person) is that you’ll need to utilize one of my “Mutliplexer SmartApps” to allow you break out each window/door into its own SmartThings “Device”. My multiplexer apps keeps “virtual devices” up to date, thereby allowing normal ST SmartApps to see each door and window as a single device. This is necessary since ST does not support having a single device with more than one of each “device capability”. My ST_Anything.ino implements one of each capability. The ST_Anything_Doors_Windows.ino example implements many “contact sensor” capabilities. For each and every “contact sensor” you define in your arduino sketch, you’ll need an entry in a Multiplexer app, and a corresponding virtual contact sensor device (manually created, as I haven’t figured out how to automagically create child devices of a SmartApp yet.)
Hope this helps. Have fun!