how hoes the eye
 

how does saurons eye see everything and how did he find out frodo had it in the shhire

It does not see everything. He can see a lot through the palatir (a seeing stone built by the elves, perhaps by Feanor I am not sure, its like a crystal ball), but he can only focus on a small area at once. He knows the ring is in the shire because he captured and tortured Gollum, who knew that bilbo had it last. At least I assume thats what you mean by It.