I've been a temp for about 7years now. It pays the bills. How it works is you can register free with multiple agencies. Most like you to do it online but I'd follow up with a phone call and alert them that you registered and are interested in getting work. Many will also do permanent placements.

They will then ask you to come in and do some testing. Usually stuff like grammer, spelling, typing speed, and some software packages like Word and Excel especially.

You will then meet with a consultant and you get to talk to them about what you are interested in, what your salary expections are, areas that you can easily travel to, etc. and they can tell you what is expected of you as a temporary employee and what they can provide to you
If a job comes up that they think you are qualified for, they will then call you and talk to you about and let you know what rate they can pay you for the position and how long its for. Don't expect the same pay rate as you will get as when you are a permanent employee though.

If you are interested in the contract, they will then send your resume to their client, if the client is interested, some will then want to still meet with you first for an interview, others will trust the agency and the resume and just offer you the position without the interview. Contracts can be anywhere from 2 weeks to a year but I find most are for 3 months, then if they need you longer, they will then ask to renew you. I was actually hired for a 48 week contract with Department of National Defence. My contract is finished April 12 but they've asked me to stay another 48 weeks. I let my agency know but asked for a $2/hr increase and they said they could only give me .75 cents so I shopped around and ended up going with another agency that was willing to pay me the extra $2/hr.

The agency negotiates a rate with the client then they take anywhere from 25% to 33% of that money for themselves and you get the remainder. Not sure how it works in the U.S. but we also get an additional 4% vacation pay plus the agencies have to pay us for statuatory holidays out of their pocket. The client doesn't have to pay it though.