Hi,
I'm not a musician but I would like to try to use my old B&W with Echo Mia MIDI card for some music What except mentioned hardware do I need and also what software can be used?
as a non-musician you likely don't have a midi keyboard and no external midi soundmodule either, so the card is pretty useless.
It does no sound on it's own, but transfers sound control data (midi) from the Mac to external devices or receives such data from external keyboards.
To make music with just the Mac on it's own no additional hardware is required.
(it has an onboard sound and can do it all in software out of the box)
The quality of that onboard-setup (you guessed it...) varies with Mac model and covers basic listener demands, but of course it's not studio grade.
So anyone who wants to produce his/her own music with better control and output quality extends the machine by an Audiocard or combined Audio/Midi card. Those devices can also come in form of an external box connected to Firewire or USB ports.
There's a wide variety of setup options, from 20 bucks upto 20k...