Yes you can read it online, rather than posting links I'll leave it up to you to Google "AA Big Book online", there are quite a few sites that have it including AA's own site.
Most bookstores carry the book Alcoholics Anonymous, and it's commonly sold at most AA meetings. Used bookstores normally have at least a few copies.
It's very helpful to have a sponsor and attend meetings as you journey through the 12 Steps. The Big Book tells you how to do it, but it's definitely recommended to have as much support as possible and the guidance of a sponsor.
Keep asking questions and reaching out for support. That's what we're here for, and what Step 12 is all about.