Recording audio from an external source (such as a microphone or a guitar) to your computer can be confusing.  There are many articles on the subject, each with various approaches.  To make things simple and relevant to Kompoz, we'll discuss only two options.  They are:

1. Using a microphone
2. Using an external audio interface device

If you're a vocalist, then option 2 (audio interface device) is not an option yet -- at least not until scientists figure out a way to plug humans directly into into our computers.   So let's start with option 1 -- using a microphone.

Using a Microphone

Standard XLR Connection	Most professional stage microphones use an XLR cable, which have connectors that are circular in design, and have between 3 and 7 pins. These types of cables cannot be connected to your computer directly; however, there are many external audio interfaces designed specifically for this purpose. If you're using a microphone with this type of connection, you'll want to read the next section titled "Using an external audio interface device".
Mic with USB Connection	You can purchase microphones with a USB connector, allowing you to plug it directly into your computer without the need for an external audio interface. If you're using a micorphone with this type of connection, you're all set. You do not need any additional hardware.
XLR-to-USB Connector	And finally, if you have an existing XLR microphone and you do not want to invest in an external audio interface, you can by an XLR-to-USB connector. Connectors, such as the Blue Microphones Icicle provide the needed phantom power. If you use a connector like this, then you're all set. You do not need an external audio interface device.

If you have a USB microphone, or a cable that converts your XLR to USB, then you're all set. You don't need any additional hardware. But if you do have a XLR mic, or you're trying to connect your instrument (guitar, bass, etc) directly to your computer, you'll need to buy an external audio interface. Fortunately, these are relatively inexpensive and easy to find.

Using an External Audio Interface Device

You can't plug a guitar or XLR mircophone directly into your computer. You'll need a special piece of hardware that converts the relatively weak line-level signal from that instrument into a digital signal that can be processed by your computer. These hardware devices are typically referred to as audio interface devices, and a simple Google search will show thousands of results. Most are relatively inexpensive, ranging from under $100 USD for simple devices, to several thousand dollars for rack-mounted studio-grade devices. For the home recording market, the most popular devices sell for about $200 - $300 dollars.