Song volume question

there is a mastering stage or pre mastering stage compressor, linear eq and a limiter these are some plugs that would go on the master bus after mixing down to a stereo file.  usually I would mix down bring that file into another new project file and pre master there. this would help with volume on final mix down but you should not have to do any major fixing if it is mixed well. look up info on mastering

If you are playing your song against commercial music you have a long row to hoe (you should know that expression, Agentcalm, being southern and all). 
 
Mixing loud is the first step.  For rock stuff, that ain't hard what with all the loud guitars and big drums.  It is when you switch to quieter styles that problems come in.  Getting a ballad to match the loudness of a rocker either side is a trick.  Mix loud, probably to -6 to -3 dB maximum.  The next trick is to get sustained loudness, which is where mastering helps.  There are plenty of threads on that and like all professional aspects, it takes time to learn the techniques and then learn to apply them so you develop a style.  Just slapping a brickwall limiter on everything will sound, well, bad.
 
The last thing is that every song balled up to -.01 dB sounds, well, bad (to me anyway).  You should get close, but having a few dB of dynamic range can really open up a song.  The stuff from the 60s and 70s and later sounds superb because it does have dynamics.  Most modern commercial stuff sounds like a boa constrictor squeezing the breath out of a small mammal.  You don't have to go there - there is a thing called a volume knob.  A small twist will make your song even louder than metallica.
 
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Howdy AT , CJ
AT, no i hear ya partner, I'd be silly to trying to compare my home efforts to a professional CD.
No i was just curious if the volume of my final MP3 depended simply on the volume setting of the master fader.  But it seems from the replies it also has to do with mastering (thanks CJ).  Truth be know, the row i gotta hoe is a might longer than long.  My mixing skills are very much beginner so I'm a ways of learning mastering.  I'm just a bit down and concerned about the recording as I just had one of those emails from TAXI telling me I'm as talented as a dead monkey.  You start to doubt everything when you get these rejections.   For now, i'll work on the mixing skills and just turn up the ITunes volume.  Right now mastering for me is a ways down the road n over the horizon.
Thanks again y'all for the replies n advice. 

If you are exporting "what you hear" or "main outputs" then the master bus fader (assuming you have one, most project templates do) will affect the output volume. The better option in this case is to set the actual output fader lower (in the console view), keep your master bus fader at unity and when exporting select "master bus".