Straight from peopleperhour website 

"People per Hour is the online marketplace for freelance services. People per Hour encompasses a wide variety of services, ranging from administration, research and writing to graphic design, web development and marketing.

People per Hour enables small businesses and busy individuals to get projects done in an easy, cost-effective and transparent way, without the trouble and cost associated with employing someone full-time to carry out these tasks. People per Hour‘s model allows businesses and individuals alike to remain flexible and get work done on demand, at the same time bringing new work opportunities to a global network of specialist service Providers."

Anyone can go and post a project on the website. It has two options:
1) Standard listing, which is free
2) Priority Listing with a posting fee of £4.95

Peopleperhour has a money back guarantee if you post a project using priority listing and don't receive any bids for your work.

Once you post your project then you select a supplier from the bids you received. After selecting the bid you deposit a minimum amount and the money is handed over to the supplier only if you are satisfied with the work done.