http://freedsound.com/

What does this website do? This is really simple, it lets you download any song and video that's on youtube, you don't need to past any link or to convert anything, you just have to insert the song/video name in the search box, you click the search button, you open the content you want and you finally choose what to download either a video or a music.

Let's do an example.

Let's say I want to download one of Ed Sheeran's famous songs, let's get for example Galway Girl, so what to do?

First of all, let's type the song name.



Now, as you can see, we've got a bunch of results, we choose the one that we want and we click the musical note icon.



After we click it, we'll get on a new page, the download one, now we've to click the big blue button with "Download MP3.



Now we've done, you have your song downloaded, it's really easy, it could happen that when you try to download something an advertisement page pops up, but you can just shut down it and you proceed with the download.
This is the fastest and the easiest mode I know for downloading music, in my humble opinion this guide is faster than the others existing like the youtube converter ones, now it's up to you what to use, your choice!