Google Science Fair is one of the largest science competitions where students showcase their projects. To participate in the competition, interest applicants can submit their projects till May 18, 2016. Regional finalists and community impact winners will be announced on July 18, 2016 while global finalists will be announced on August 11, 2016. Awards to novel and revolutionary ideas will be given away on September 9, 2016.
The competition is free for everyone and all the details related to the Google Science Fair can be found here. https://www.googlesciencefair.com/en/participants/faqs
To know more about finalists from previous years and their projects see https://www.googlesciencefair.com/en/competition/previous-years