CELEBRATE! Seriously, this is a major accomplishment and you should be very proud, happy, excited, etc.
Timelines vary widely, but here are some other things that happen when/after you get an offer/book deal:
They'll tell you when your book will tentatively be released. The typical book release schedule is 18 months to 2 years out from your sale.
BUT they may decide to "crash" your book, which means they put it on the schedule for a year or less out from offer–which means everything will happen VERY FAST and you'll have to be ready to dive into next steps right away.
Your agent will introduce you to your editor, usually via email. Then you can have a phone call with them/get to know them, etc. Some agents will simply hand you off and ask you to CC them on anything vital/important, but otherwise you own the relationship with your editor. Other agents will want to be copied on every email with your editor. Ask your agent what their style/preference is (on the offer call, ideally)!
(Eventually) Sales & Marketing will have you fill out an author questionnaire where you tell them EVERYTHING about you and your background, to help them position your book. Be ready to draw on allllll your experience and contacts through out the years. They can use it all!
You'll announce your book... either fast or slow, depending on the circumstances. Some publishers don't let you announce until the contract is complete, and contracts can take months. One author I know had to wait eleven months to announce... this is not typical, but it does happen! Other publishers will let you announce as soon as your agent is happy with terms, ie: quickly. Ask your agent about the timeline!
I'll be covering everything that happens when you have a book deal in much greater detail in the Book Deals & Marketing edition of #HowToAuthor.

YOU ARE READING
#HowToAuthor: Agents & Submission
Non-FictionAdvice for writing book-shaped things and getting them traditionally published. This series will cover everything from querying to agent fit, to building a platform and marketing yourself.