Occassionally people write with issues when they try to download a product directly to an iPad (or smartphone) by clicking the link in the order e-mail.
Unfortunately, you can't download products you buy online to directly to an iPad. (key word is directly) iPads don't work like computers, they don't have a file structure, so they have no place to "save" download files in the traditional sense. When you watch files online, they are 'downloaded' only temporarily to a hidden 'cache' - similar to RAM on your computer - after you watch, it is gone. (That's what buffering is, you are waiting for it to load to the cache)
BUT you CAN get a video onto your iPad, if you want to watch it there or perhaps to take on a mission trip! You just can't use the download link from when you buy a video. (from any website)
Here's what to do: You need to download the video to your computer and then put it into iTunes. From iTunes you can sync your iPad and select which videos you'd like on your iPad - during this process they are actually put into the memory storage of your iPad. (Depending on the size iPad you bought, 16GB, 32GB etc. - you just have to have enough space for it.) That memory is called ROM - I may bore you (but I like this stuff) but let me explaint he difference between RAM and ROM. RAM = Random Access Memory, its there, and then its not, kinda random, but ROM (your hard drive or iPad memory) = Read Only Memory - it reads and uses whatever is saved there, apps, videos, music, etc. You manage ROM the device manages RAM.
I hope I this isn't tooooo technical for you, but sometimes it helps to understand how these tools works rather than just saying, "you can't download to an iPad, you must download to a computer and transfer to an ipad" that the short way of saying it. :o)
If you have any further questions, don't hesitate to ask us. We are here to help!