1. There is no correct steps by steps to learn siebel as we can start learning siebel from any corner.
2. You can try bookshelves for materials. For starters try doing siebel configuration.
Do try creating your own custom , table , bc , applets for beginner.
Or if you have the oracle training slides you can follow it. Its really helpful.
For learning you can get all the source material from the edelivery website of oracle.
I would recommend downloading the Siebel Client and the bookshelf there.
Try out configuration using the sample data that is there in the various downloads and try checking out the various views in the Siebel Client and the corresponding setup in Siebel Tools to be able to learn better.