What software are you using? You can buy a hardware or software sampler or other software like Reason or ACID, but all of this can get expensive fast--especially when you add the cost of sample and/or loop CDs.
A less expensive route is to use a a basic audio/MIDI sequencer and a $35 Soundblaster Live card. You'll be able to record both audio and MIDI with the sequencer, and with the Live card you can load soundfonts to use for the sounds of your MIDI tracks. Note: you will need a sequencer for multi-track recording. They cost between $50 - $1000. I hear N-Track is useable. I like Cakewalk products, and they have some inexpensive ones, like Guitar Traks or Music Creator.
Here's an example (assuming you already have equipment--microphone and preamp--to record with) of how you would arrange/record/mix a song with a sequencer and soundfonts:
Once you have written the melody, lyrics, and chord changes to a song, go into your sequencer and score/create MIDI drum and bass sequences. Now you have one MIDI drum and one MIDI bass track. You have a lot of soundfonts (acquired free) to choose from, so you have a choice of acoustic, electric, and synth basses and drum kits.
Next you play back the drum and bass tracks through headphones and record your guitar rhythm and lead parts to seperate audio tracks. Now you have a total of four tracks, two MIDI (drum and bass) and two audio (guitar rhythm and lead).
Next you record lead and backup vocals in the same way you recorded the guitars. Now you have a total of six tracks: two MIDI tracks and four audio.
Next you turn the two MIDI tracks into audio by recording them onto two audio tracks. Now you have six audio tracks. Mute the MIDI tracks, but don't delete them.
You add more MIDI tracks as the song needs (brass, woodwinds, pads, etc.), and record them as audio.
Next you mix all of your audio tracks by panning (placing) the various instruments left or right in the stereo field and adjust the volume of the instruments so they sit (back, middle, or front) of the mix.
Next you can add effects to taste. Most recording software comes with at least basic FX, and you can add more later.
Finally, when satisfied, you mix down all tracks to a single stereo file (two tracks), save the file as Mix 1, and burn a CD.
Congratulations, you have produced your first home recording.