Serena I have used several in the past to get jobs, such as Kelly.
You call them and make an appointment. They interview you to find out your skills - can you type, can you take shorthand, what office equipment can you use, have you ever worked in a factory, etc. etc. etc. If you can type, they'll give you a typing test to determine your efficiency. They may give you a grammar test, etc. It all depends on what type of job you want.
Then they will try and match you to a job based on your skills. The job could be for a day, it could be for months. They will tell you up front what the job pays. You do not have to accept it if you do not want to and that doesn't count against you.
On several occasions, I was sent to jobs that were unfilled positions at companies. Usually someone left suddenly. They liked me and offered me a permanent position with a salary. I accepted the permanent position and left Kelly. There was no fee due to Kelly for this.
On a few occasions, I was offered a permanent job which I didn't want. I just told them I wasn't interested for whatever reason and kept working through Kelly.
You will be required to fill out a time card for each job and the supervisor at the company has to sign it. You turn it in on a certain day, and Kelly gives your your paycheck.
Most temp agencies work the same. A temp agency is not the same as a job placement agency; job placement agencies try to find you a permanent position for a fee. If you use a job placement agency, make sure you tell them you are looking for a fee paid job only (this means the company who hires you pays the fee, not you). You are usually required to stay with this company for at least six months; if you leave before the six months are over, the company can demand you refund the fee they paid to hire you. Snelling & Snelling is one of those types of companies, if they are still in business. I don't know; I haven't used one in a long time.
Register yourself at monster.com and search for jobs in your area through that also.
hotjobs.com too
PM me if you need more info.