The WiPy is a microcontroller that runs MicroPython on a light-weight processor along with a WiFi chip so the device can communicate with wireless networks. As a matter of fact, the device pretty much must communicate with wireless networks since that's how you interact with them.
The WiPy is one of a growing selection of possible MicroPython boards that you can use for experimenting, programming, and/or Internet of Things development (but more on security later). The big ones seem to be the WiPy, the PyBoard, and the ESP8266-based boards (such as the Adafruit Feather Huzzah! ESP8266 or the Huzzah! breakout), though the microBit is likely going to be a player, particularly in the UK, because of its deployment footprint.
This guide is about the WiPy, but for information about the overall MicroPython ecosystem check out Tony DiCola's excellent series of guides - there's a list on the "Additional Resources" page. Also, a big shout-out to Tony for the fantastic work on MicroPython, including his guides and streaming videos.
The WiPy can be purchased and used on its own without anything but a USB cable for power. There is also a no-soldering expansion board that includes a micro-USB connector, a 2-pin JST for a LiPo battery, the necessary LiPo charging circuitry, and a micro-SD card slot for storage expansion, on top of the GPIO pin breakouts.
While you're ordering the WiPy and the expansion board you can pick up a LiPo battery of an appropriate size for your use. I use a 6600 mAh three-cell pack from Adafruit and I honestly haven't run it out of power yet. I'll test it to see how long it will run with that battery, but it's going to be a good long time.
When the LiPo is plugged in and the USB is connected to a power source, the onboard charging circuit will keep the LiPo topped off. The LiPo battery support is handy for when you want to take your project mobile!