Adjustments in computer settings to improve loading of YouTube videos

My question may be completely misguided. If so, it stems from my slender knowledge of the entire process. I have a friend who cannot adequately open the YouTube links I send her. I'm wondering why, and I'm also wondering if she might improve things by some simple changes in her computer settings. I believe that YouTube videos are "streamed" and that some ccmputer/Internet capabilities are inadequate for the task of viewing long, streaming videos. That's fine, but what about "loading"? One is constantly confronted by this term while downloading something from the Internet. My question is, once something is downloaded into a computer, shouldn't it be ready for viewing? In other words, if a five-minute video takes one-hour to download, does the one-hour downloading period make a difference? Isn't the fact that it has been downloaded the only important thing? Further, what, if anything, can the computer owner do to improve/make possible the video viewing experience?