Here's the way it generally works:
When you sign a record contract, you may or may not be given an advance. The days of the million dollar contracts are over. If you get any advance, you're pretty lucky. You are given a budget with which to record an album. From that budget, you have to pay all studio costs, instrument rentals, food, travel, living expenses, producer costs, etc. Your producer may also take a percentage of your royalties later in addition to being paid up front. Then basically, you are given a percentage of sales, less returns. Big artists might get 18%. Unknowns might get 8%. Your percentage is less for foriegn sales, record club sales, discount sales, etc. Basically you only get that big number for straight B&M sales. Your percentage is further reduced by the producer taking his cut, and further reduced by "packaging costs," which are a ploy to skim money off the top (sometimes 30% of the purchase price). They may also reduce it for "breakage" or other shady reasons. Basically, they go out of their way to make it seem like you will earn a lot but ultimately you are getting practically nothing. From your practically nothing payments, you must pay back EVERYTHING. Your advance, all those recording costs, the producers advance, travel, and often promo and other things all must be paid back to the label before the musician sees a dime. Keep in mind that this could be $300,000 or more for a big album. Also remember that managers take a cut, so he took a cut of your advance, and will take a cut of any royalties you see (if you're lucky enough to see any). If your band breaks up before the label recoups expenses, you have to pay them back. If your album is rejected, you have to record it again at your expense. If you played a cover, you have to pay residuals to the writers for every album you sell with their song. Etc, etc.
If (this is a big "if") the artist was smart enough to retain the rights to their songs, they will earn a small amount of money from radio play (like 8 cents per play). But if you have a publishing deal, chances are the publishers are taking their cut. Not to mention that most new songs you hear on the radio got there because of either flat-out bribes, or paying radio promoters lots of money to push the song. And the artist will pay that back out of royalties. Music videos make a little money because the stations pay to license them (if you're already big, otherwise you may be paying them), but not nearly enough to cover expenses. Guess who pays for the video? The artist!
As mentioned above, the only way artists really make money is by playing shows and selling merch. Of course the merch company, the booking agent, and the promoters will all be taking their cut. And you have to pay your road crew, and pay for the trucks and buses, food and lodging for the whole bunch, gas, equipment rentals (lights, stage, and sound), venue rentals, security, etc.
If a musician gets lucky or is smart, they can make a living. But most get screwed one way or another, and most new big artists tend to live outside their means to maintain their image. 50 cent will be bankrupt in 5 years (just look at MC Hammer).
But don't take my word for it. Read this article written by one of the top producers in rock music, Steve Albini:
The Problem With Music.
So next time you watch the MTV Video Awards, remember that nearly everyone you see is broke.