A typical studio microphone (dynamic or condenser with XLR cable outputs) requires 2 things:
1. Mic Preamps - To amplify the weak mic signal to a level the computer can use.
2. Phantom Power - Only in the case of a Condenser Mic.

Both mic preamps and phantom power can be found in an Audio Interface… more on those later.

Next you need to take that amplified signal (analog) and convert it to a form the computer can understand (digital). This is done by Analog / Digital converters. These can be found in an Audio Interface or Sound Card.

In the case of a USB microphone… you will have the mic preamps, A/D converter and phantom power built right into the mic itself. The USB mic plugs directly into your computer’s USB port and is a very quick and easy solution. It’s the easiest way to get started but there are some drawbacks such as limited mic selection and being limited by number of USB inputs to your computer.

Mixers have mic preamps but not A/D converters — so keep this in mind when picking out gear. They can be used to control the levels of each input, the levels going out to your monitors, and the levels going out of your main output. Digital versions connect via USB or Firewire and may have some FX (flanger, chorus, reverb) built in. If you opt not to go with a Mixer that’s ok… you’ll be able to adjust levels via Software included with your Audio Interface.

With your current gear you will only be able to record 1 input at a time (via USB condenser mic) which may or may not be a problem for you. If you want to add more mics then your best bet is to get an Audio Interface with enough inputs for your needs.

Audio Interfaces are available that have several mic preamps on board. Remember that for every mic or guitar that you want to record via its pickups you will need a mic preamp. So for 2 condenser mics and 2 guitars with pickups you will need 4 total.

That should be enough for a start. If you want to record your guitar directly into the Audio Interface without using a microphone you can get a Direct Box (sometimes called a DI Box) and plug your instrument directly in.

As far as actually recording, almost every Audio Interface or USB mic will include some basic software that will be enough to get you started out of the box.

Finally in terms of pianos — if you are talking about an acoustic instrument then you can use the mics to record the sound. If it’s a digital piano or synthesizer you might consider a MIDI connection which is an option on some models of Audio Interface and Sound Card as well. MIDI is a versatile and valuable tool for creating music and can really expand the capabilities of a home studio.

have fun and good luck
References :
http://www.basic-home-recording-studio.com

If you want to do anything more than simple mono tracking, you’re going to need an audio interface. This will allow you to plug a bunch of microphones into it at once and record them all (critical if you want a good drum sound)

There are quite a few options out there and most of them will run well with your Macs.

I’ve been recommending the new Tascam US-800:
http://recordingquestions.com/gear/tascam/us-800/599

It’s the best bang for your buck out there right now. With 6 mic inputs you can get a decent drum recording you just need to pick up a little drum mic pack like this:
http://recordingquestions.com/gear/cad/cad-pro-7-drum-pack/729
References :