The power button of the iPad is located at the top right corner. Press down the button for 5 seconds, till the "apple" icon appears.
If a blinking battery is shown instead, your iPad is not having enough battery backup and it needs to be charged.
Use the power adapter that came along with the iPad to recharge its battery.
A full charge would take anywhere between 1-2hrs.
Once the power is back, the iPad will start automatically.