Question

how do i start

Answer 1

Read the book. then read it again. And then, read it again. Read it again and again. And I mean it. SICP isn't an easy-in.

Answer 2

Read the book SICP, supplement that with the video lecturer available online. I have completed chapter two and working on the problems. My personal opinion is that if one has programmed in any language then reading chapter1 and chapter 2, running all programming wouldn't take much time. Even doing question at the end of chapter will be easy but they will take time. But chapter 3 and following chapter are tough. You may require it to reread. You can also supplement the SICP book from the Berkley's SICP course. If you are having difficulty learning scheme language you can use the http://www.cs.berkeley.edu/~bh/ss-toc2.html book to supplement.
This link berkley SICP course web page and all other information.
http://inst.eecs.berkeley.edu/~cs61a/sp11/

If you still have any doubt, you can post it here and other will help you.