While I agree wtih what has been said so far in this thread, I will try and explain a bit about why it was said. Learning the sword arts (Japanese in particular) is an esoteric undertaking. The sword (for the most part) is no longer used in today's society, so the nuances of how to use the sword have been pretty much lost except for the legitimate Japanese sword arts, and the few historical European sword art schools that have been re-learning what was written by masters in the past. Contrary to what you would imagine, the proper way to use a Japanese sword is NOT natural. The movements are counterintuitive, and the musculature developed is not usually used in other endeavors. It feels very awkward until you've practiced enough to make it feel natural. This is the primary reason that people say you cannot learn without a legitimate instructor to guide you.
On the other hand, there are a number of places that you can buy a Japanese style sword of acceptable quality, and even more where a bokken (wooden practice sword) can be had. There is nothing wrong with buying a bokken with a saya and imitating what you see in a video for your own entertainment, as long as you are careful and play safely. Just be aware that you are NOT learning a Japanese sword art, and you'll have to unlearn quite a bit if you decide to actually join a legitimate school later on.