Before the invension of peer-to-peer transfer protocol, there was only one way to download Hindi songs, as an individual mp3 file for each song. The disadvantage with method was that, the downloads were not resumable - as some sites explicitly blocks this and it wouldn't work with older web servers.
With the invension of torrents, sharing the content across the world has been simplified. There are 3 major steps to start using torrents.
1. Download and install torrent agent, such as micro-torrent, bit torrent or any other torent client.
2. Open a torrent search website, (torrentz.eu is one that I use regularly) such of Search for the name of the movie followed by the keyword "songs" in as one of the torrent search crieteria. Eg. "Kuch Kuch Hota hai songs". Or just search for "download hindi songs" or "bollywood songs". You should be presented with various torrent websites and I shall update shortly with us
3. Download the relavant torrent file and double click the *.torrent file. It should get opened with the torrent cllient that you installed in step 1. Alternatively, you can just click on the magnetic link icon which looks like an inverted 'U' (horse shoe) shape.
Follow the onscreen instructions, in general, you will need to specify the download location.
Here is a quick location where you can search whatever you want. https://torrentz.in/search?q=hindi+songs Please ensure that you are not violating copy rights while downloading. You are not legally allowed to download the content, unless you have paid for it.
For example, if you have bought songs of a movie, say, Piku, only then you are legally eligible to download a copy of the songs in MP3 or any other format, just for the use by you in your music players, such as MP3 player, an iPod or a mobile phone.