This site is like any other youtube to mp3 converter: it needs your input to provide results. And so you'd need to know what youtube URL you are trying to convert to mp3. This article on google perfectly explains how to Copy Video Link into device Clipboard. Usually you'd have to click (or tap) Share button right below the video. In the menu that opens up, you'll select Copy Link - for desktop. Mobile simply opens standard share menu, that has Copy Link to Clipboard as one of the options (for Android). After that all you do is open our Youtube to Mp3 Converter, right click (or tap and hold) on the box in the center of the page, and in the menu that shows up select Paste. That's all there is.. Now click GO and mp3 download buttons will appear. Either of the 2 buttons works great. We place 2 just to make sure there's always 1 that works, if the other goes down.. Buttons may sometime take 10-15 seconds to do their work, but download usually starts on its own..
In reality, there's no certain law stopping you from downloading youtube videos and converting youtube to mp3. There's this thing as Youtube's Terms Of Service (TOS), that specifically indicate that you are not allowed to extract and/or somehow download video or audio data. So the worst that can happen to a random user like you is a wrist slap. Downloading youtube videos and converting youtube to mp3 is not a crime. It is litterally a violation of Youtube's TOS. That's all!! Worst case scenario there's Civil Court that could give you some civic duty fine... That is if you go around agitating others to convert youtube to mp3 and break the TOS afformentioned.. so basically don't be proud of this activity and you'll be OK.. and try to download copyright-less videos and their audio, there are tons of those.
That maybe due to the fact that you're on an Apple device or system. Apple are very stiff about mp3 and video downloads to their devices. They want all of the media to go thru iTunes and register in libraries and all that stupidity. All internet browsers are to comply with that, thus it is soooo silly hard to download mp3 from a website on your iPhone. There are many resources explaining how to circumvent that restriction.. Check out this guide or this one right here explains how to download any files on apple systems and devices..
If you are not on something made by Apple, you should be able to download file easily. If clicking the button doesn't do it, try to Right Click on it and in the menu select Save File (or similar link, depends on system). If you are mobile, Android does it properly too. Simply touch and hold the button until context menu pops up, in there find Save Link option and go with it!
This depends on the system/browser you are using. Most of the time it will be Windows or Android. So we will give info on those 2. Windows has main Downloads folder, but technically browsers save files to the Last Selected Location. If you never changed that location, it'll be the default downloads folder for the browser. Here's a detailed guide for windows. And for Android things are a bit different. There's also that folder, but accessing files on Android is not a normal procedure, so you'll need additional apps for that.. Unless you are trying to find those files via the media player you like.. Then it's different.. Folders and situations are there too.. Check out this Google's guide on how to manage your files on Android.