But if you're getting started as a professional musician and you have a budget of basically zero dollars to allocate toward the recording of a demo. If that sounds like you then you'll want to keep reading.
There are several ways to record a decent demo for the purposes of getting gigs without breaking the bank.
1. If you're interested in learning some basic recording software you can download the open-source recording software Audacity for free. Audacity will allow you to record your instruments and edit your tracks through the computer's line-in input jack. Once captured in the computer you can manipulate your sound add effects and multiple parts and finally burn it to a CD. I will say that this does take time to learn the software and get familiar with it's strengths and shortcomings--which is true of any recording equipment you attempt to use.
2. If you have a four track cassette recorder--I know it sounds ancient, but they're still around and they can be a decent medium to record on for a basic demo. Hey, a four-track is all the Beatles used for the majority of their hits. My advice if you use a four-track cassette recorder is that once you have your tracks where you want them play it back while recording it into your computer, and if you use a software like Audacity you'll be able to tweak your sound and EQ it, and once in the computer you'll have a digital copy of your music that you can burn to disc.
3. If you have a Mac computer. It usually comes equipped with the iLife suite, which includes Mac's own basic multi-tracking recording software, GarageBand. GarageBand is pretty robust for how well Apple has simplified it for those who are new to digital recording and mixing.
4. When all else fails grab a decent stereo with an auxiliary input and a tape cassette. Grab an external microphone to plug into the auxiliary input, find a bathroom in your house with good acoustics and play your songs live into the recording stereo. Get it to a friend if you're not good with computers to have them get your song from your cassette onto the computer to "digitize" it, so you can burn to a CD again and again without generation loss.
5. Another way to get a digital signal of your music is to use your digital video camera to record your live performance. This can serve a dual purpose of capturing a video of your song that you could post to your website, but also you could pull just the audio portion from the video to use as a demo. Most hand-held digital video cameras have pretty decent sound these days--often about 16 bit sound, which is pretty remarkable for such small devices.