Connect your sound sources to your computer via the digital interface. Keyboards, electric guitars and basses can all be connected directly to it via 1/4-inch instrument cables. For vocals and the recording of acoustic instruments, you'll need to connect a microphone to the interface using an XLR microphone cable.
Arm your first track to "record" and adjust your levels so your peaks are around -12dB. This should help you avoid peaks above 0dB which results in an unpleasant digital distortion known as "clipping." You can then record your songs track by track, using your instrumentation of choice. When you've done this, your tracks will be ready to mix.
Adjust the level, panning, and equalization (EQ) of all of your recorded tracks until you're happy with the mix, and save it as a stereo WAV file.
Master your recordings to give them a little polish. Mastering should make your collection of songs sound like a cohesive whole, with smooth song fades, consistent volume across all songs, and tasteful use of effects like compression and EQ. Mastering is a specialized skill, so if you intend to sell your CD, consider having your mixes professionally mastered to make it sonically competitive in the marketplace.
Burn a copy of your master recording using the CD burner in your computer. If you're going to use the CD as a promotional tool, this should work fine since you can burn them as you need them. If your intent is to have copies for sale, send your master to a manufacturing plant. In this case you'll send them the copy that your mastering engineer sent you.