Session Musicians: What Do They Do?:
Session musicians are essentially "for hire" musicians. They perform with solo artists and bands, but they are not officially part of the group. Session musicians play on recordings, play in live shows or both. Although some give and take may happen during recording, session musicians usually show up and play what they are asked to play. In other words - they don't write the music, they play what others have written.
Where Do Session Musicians Work?:
Some session musicians are tied to studios and primarily work in a particular location. Many more are independent contractors who find work by word of mouth - a studio recommends them to people coming in to record, artists recommend session musicians they have worked with to friends, and so on. Session musicians work in studios and they often go out on tour as well.
Finding Work as a Session Musician:
There was a time when labels had session musicians on the payroll as a matter of course, but when this happens these days, it strictly the domain of the majors. As previously mentioned, most session musicians get work by work of mouth. The best way to keep steady work coming in is to work on your reputation as the go-to player for your instrument in your area. Getting local studios on your side and building a relationship with labels is essential - self promotion is critical to getting your career as a session musician off the ground.
You can learn more about finding work as a session musician here.
The way you are paid as a session musician can depend a lot on where you live. In some countries, there are set hourly wages for session musicians, and that's the bottom line. If there isn't one of these set wages where you live, then you will negotiate a rate for the job for which you are being hired - either hourly or a set fee. The going rate can also vary wildly depending on where you live and the project.
The important thing to note there is that session musicians do not (usually) get royalties or any other income generated by their recordings after the job is done. You get a flat fee for your work, period.
Concerns for Session Musicians:
Things can get a little complicated for a session musician if certain things aren't hashed out up front. Keep these questions in mind before you take a job - and get it in writing!:
The fee - of course you should discuss how much you're getting paid, and when.
As previously stated, session musicians are hired to play what others have written, but some give and take is inevitable. What happens if you make a significant contribution to a song? Will you be happy walking away with a flat fee for that, or will you want a songwriting credit (and royalties)? This can be an incredibly touchy subject and should be discussed when it comes up - don't assume everyone is on the same page, even if you're working with friends!
How will you be credited on the album liner notes.