Downloading mp3 to iPhone or iPad
Apple does not allow a direct download of an mp3 file, from a website, to an apple device like an iphone or an ipad.
So, if you click on the download icon using your iphone or ipad, it will just play the audio mp3 file from the website. It will not download the mp3 file to your iphone or ipad for offline use.
To get the mp3 file onto your iphone or ipad, you will need to download the mp3 file to your computer first.
Then add the downloaded mp3 file to iTunes on your computer. Then sync iTunes with your iphone or ipad. This will then transfer the mp3 file to your iphone or ipad, so you can use it offline.
I hope that helps. If you need any more help, please send me an email at firstname.lastname@example.org.