One can visit the examination calendar of the UPSC year from its official website www.upsc.gov.in.
Major examination conducted by the UPSC are following:
Civil Service Preliminary Examination / CSAT Examintion / IAS Pre Examination
IES Exam / Indian Engineering Services
Indian Forest Service Examiantion
UPSC SCRA Exam for Special Class Railway Apprentice
NDA and NA Exam
Many other examinations which you can refer from the website of UPSC.
You can apply online, download information related to admit card / hall tickets, examination schedule, past papers, syllabus and much more from the official website: http://upsc.gov.in/
You can find the new events / updates about UPSC in What's New Section: http://upsc.gov.in/whatsnew.htm