same usb cable you used for charging should do.
iTunes on your computer
Edit:
What you basically want to do is completely wipe the iPad's software; you do that by holding Home (the big button at the center bottom of the screen) and Power _forever_ - until you see something like this*:
https://support.apple.com/library/c...phone_se/iphonese-recovery-mode-tech-spec.png
that tells you: "connect me to itunes"
so you'll need itunes on your computer. then itunes we redownload the OS for you and install it on the device. Then it's brand-spanking new (software-side) and all yours to break again
* really forever; don't get distracted by what the device does. it'll reboot at some point - just keep holding, it'll eventually kill itself and pop to the "connect me to itunes"-screen
edit2: if your cable can't do data/only charge. you need something like this:
QVS USB Charge and Sync Cable for iPad/iPod/iPhone-AC-1M - The Home Depot
(if it's really an ipad 2 with the old (wide) connector; if it's a new one with a small connector you need this:
https://www.walmart.com/ip/Apple-Lightning-to-USB-Cable-3-ft/21853452)
but usually the one you charge with should do