How do I add memory to my iPad 2?

You don't. iDevices don't have expandable memory.

You can look for a device like the Kingston WiDrive, which is a portable drive that you connect your iPad to (via a wifi network created by the drive) and you can stream media and transfer files that way.

Apple doesn't allow to use external drive to add memory. If you want to increase your storage space do following thing

First delete all unnecessary files from your iPad now transfer important files to mac or PC now you have more space to save your new data.

Other wise you can buy space on iCloud and save your data on cloud storage always accessible data easily.

Not true.

I am using a portable WiFi 500 GB hard drive from Seagate on my iPad Pro.

I have ALL of my movies stored on this drive and it works fine.

Western Digital has portable Wifi hard drives that work with iPads.

I am getting my mother a 128 GB WIFi San DIsk flash drive that will give her 16 GB iPad 2 eight times as much storage space and this drive is almost as small as most common USB flash drives.

I am using a portable WiFi 500 GB hard drive from Seagate on my iPad Pro.

I have ALL of my movies stored on this drive and it works fine.

Western Digital has portable Wifi hard drives that work with iPads.

I am getting my mother a 128 GB WIFi San DIsk flash drive that will give her 16 GB iPad 2 eight times as much storage space and this drive is almost as small as most common USB flash drives.