Young Adult Book Reading Challenges discussion

I have just finished this book and I have so many questions about the rules of the time travel, I have yet to read the third book and I know that that will answer all my questions but I cant read it yet and so I really need so answers now without any spoilers! For one I dont understand how there are two different timelines and what happens to the world B when he goes back to world A? What is a Thomas-Jump and why can he see himself in a thomas-jump? What happens to the other him if he stays in the thomas jump? What is a complete jump? what is really the difference between eyewall and the EOT's? God I am just so confused!! If anyone could help I would really appreciate it!