Google market place is Google's web interface tool by which web publisher and advertiser can come on single platform.If a web advertiser using Google's services to advertise then he can choose a particular size buy ad space on that site.As a publisher your site must be listed at Google market place, then only it will be visible to advertisers. I hope this gives you some basic knowledge about Google market place.Although there is lot more about it and can't be explained in single post.
Google market place is the place where you can look for your product and buy it if it suits your need. it is also essential tool for the product promotion. it mostly use the google base feed for providing the product information.
Additionally, Google market place or Google Base is an extremely helpful tool for E-Commerce websites.
Is this different from Froogle - Google's product search? Or is Google Market place refers to a group by which advertisers have options how to market their products like through Adsense, sponsored link on Adwords, etc.? Thanks for more information-rich feedback guys.