hi mate,
the easiest way to get music onto your Asha 201 is to buy an external microSD memory card, say a 8GB or 16GB one (that will leave you with plenty of rooms for all your songs), and leaving your music in MP3 format is perfectly fine, as your device plays this format of audio files. I would invest in the cheapest, reliable-branded memory card, e.g. SanDisk, but not buy a Class 10, a Class 4 or Class 6 memory card is just fine. If you are not sure what Class refers to, check Wikipedia.
Simply insert the memory card in the phone, and connect your phone to your PC using a microUSB cable, and select Mass Storage on your phone when prompted. Copy the music (preferably in folders so that you know where all the music is, and organised) to the memory card, and then safely disconnect the device in Windows Explorer. Goto the music player on your phone, and if it is not already refreshing the music library,then select this option in the Music Player settings.
Bingo, now play your favourite jams!