The PowerBoost shield is fairly easy to use, and is mostly plug-&-play. Here's a quick review of what you can find in your shield
This is the workhorse section of the shield. It takes the 3-4VDC in from the LiIon/LiPoly battery and boosts it up to 5.2V DC. This section includes the control chip, inductor, some resistors, and output capacitor/fuse/diode.
To protect the booster and battery, we put a 500mA fuse on the output of the boost section. The fuse will trip when a continuous current higher than 1A is detected.
There's also a Schottky diode on the output, which will drop the 5.2V from the booster to about 5V. (It can dip down to 4.8V when over 1A is drawn!)
There's two booster indicator LEDs. The blue +5V LED lets you know that the booster is running. The red LOW LED tells you that the LiPoly battery is at 3.2V or lower and may need to be recharged or replaced
The charging section is how you can recharge the battery. You can only charge the battery via the microUSB jack. Plugging the Arduino into USB won't charge the battery. Use any computer or wall adapter. The charge rate is up to 500mA (but may vary based on the battery state)
There's two LEDs next to the microUSB jack which will tell you how charging is going. If the CHG LED is on (yellow) that means its charging. the DONE LED (green) turns on when the battery is full.
You an charge the shield on or off an Arduino. If you charge the shield while also running the Arduino, it will act like a 'Uninterruptable Power Supply' and the battery will stay topped up as long as the overall current draw is over 250mA or so.
There's a power switch that is optional. If you install it, you can turn the booster on/off whenever you like. If not installed, the shield defaults to on.
If you would like to custom attach your own switch, solder a switch to the middle pin and the pin right below the middle pin. Any voltage/current rating is fine as the switch is signal, not power, carrying
You can use one of the Arduino's analog inputs to measure the battery voltage which can let you know ahead of time when the battery is getting low. Simply solder onto one of the solder jumpers on the bottom of the PCB