Adnetwork, Adcampaign and Adgroups????

Hi, I am newbie in PPC. I have some questions regarding it! Like, What are Adnetwork, Adcampaign and Adgroups? What are the tools to check keyword inventory for PPC? Name of 2-3 adnetworks which are already stablished right now in PPC? From where, I can come to know current bid on keyword on my ad campaign is running?
Can anybody help me? Please answer the questions if you know.

See original post by sumitt_2004