No no no, there's no such things as noob questions! They're all understandable if you don't know where to look which is especially true for beginners!
You could use Candiifaec's way but I don't think that always produces high quality off-vocals o.o;; Adding on to her reply...Generally (to my knowledge) producers will often provide a link to the off-vocal in the original song, which will most likely lead to piapro.
A thing to note is that to download stuff from piapro you need an account. With a quick search I found one here . That guide also explains what piapro is but for a quick run down, its an offical site made by the creators of VOCALOID for fan works including music and illustrations so its very legal and safe.
Alrighty to find an off-vocal lets take for example Kagerou Days. On the Kagerou Days PV , in the description there's a link "http://piapro.jp/jin_jin_suruyo" mentioned. When you click through, you'll get to the producer's piapro's page which will show you their 8 most recent posts. Then if you click that title thingy, which for Jin says "最近の投稿作品 (28)", it'll bring you to a list of works that the producer has posted there. Off-vocals will have something like "off vo.", "off vocal ver." or something of that sort next to the title.
Since I'm looking for an off-vocal Kagerou Days I made sure to copy the Japanese for it (カゲロウデイズ) then simply searched the page for it. To do that I just pressed the ctrl button and f at the same time. A little box will then come up and you can just paste the Japanese into it.
Then you just click the link to the off-vocal and download it. The download button has the words "作品のダウンロード" on it. Its the first button at the bottom on the left.
There will be some instances where the producer will provide many versions of an off-vocal, like one with +2 key or -2 key, so be sure to look out for that. A quick google translate should be able to discern which one you might want.
I hope I helped somewhat and I hope it isn't too hard to do everything I said o.o;;
Ah I should mention..."illegal" off-vocals hmm...
Usually Anime OPs/EDs can be considered copyright infringement so it might be best to avoid that...Of course I think there are ways around that since there are always people that cover them. I mean sheesh
Glutamine has over 6 million views on a cover of an Anime opening.
Also I believe that if an off-vocal is only available on a certain producer's CD, it's considered very rude to cover the song without obtaining the CD but of course I don't think the YT fandom cares too much since its really annoying (and expensive at times) to obtain the CD anyway 8D
And yes there are ways to create your own off-vocals but I won't discuss that here~
Gosh I wrote so much o.o;; I hope everything is understandable Anon!
(By the way Anon please tell me when you have read everything so that I can move the thread to the correct place. I don't want you to not be able to suddenly find it >.<;;)