It's not usually enough to persuade an editor that your book is the best thing (s)he has ever seen - the editor generally has to sell the book in-house. You don't get a contract unless the editor can persuade those who hold the purse-strings that your book is pretty damn good, and one of the best of those they have to choose from. This happens (you hope) first at an editorial team meeting and then at the acquisitions meeting. (There are exceptions; in a few publishing houses, editors have the authority to sign a book for their list without negotiating with other departments. This is how things used to be in the Good Old Days, but it's increasingly rare. These editors often wear tweed jackets with leather elbow patches. Check your editor's wardrobe to see if this is likely to happen in your case.)
If your editor likes your book or proposal she (it's usually she) will probably discuss it with other editors at a team or editorial meeting, or maybe just informally with one or two colleagues. She does this largely to get feedback and suggestions, to test her championing of your book and make sure she's not going to make a total fool of herself (for example, championing something that everyone else turned down from the slush pile if you have stupidly submitted to more than one editor at the same publishing house). Not all books go through this stage. If she still likes it, she will book a slot to present your book at an acquisitions meeting.
Publishers hold regular acquisitions meetings, but how regularly varies from one publisher to another - it may be as often as weekly, or as infrequently as every two months. At the meeting, your book will be discussed not just by editorial staff, but by representatives of sales and marketing and design, and by the publisher or associate publisher. Your editor is your book's champion at this meeting. Your book is competing with other books for the available publishing slots and budgets.
Your editor will prepare an acquisition proposal that outlines her vision for your book, why she loves it, why it will sell, a description of it (content, style, genre and also physical aspects such as page extent, dimensions, binding, illustrations, etc), and a profit and loss account or detailed budget proposal for it. She will also give an account of you, the author (and any proposed illustrator). This will cover your biography, credentials as a writer, any notable points that will help sell the book (you are very young, beautiful and photogenic, very famous, very traumatised, exceptionally ugly with freak-photo value, or press-worthy in some other regard), previous sales history (your Nielsen BookScan record comes in here) and perhaps reviews of your previous books. She will outline the terms she intends to offer you (which may well be standard) and any other relevant aspects of the contract, such as subsidiary rights, say when she wants to publish and how many copies will make up the first print run. And, of course, your manuscript or proposal will be sent round for everyone to read. Knowing all this will go on should feed into your next proposal and what you tell your editor about yourself. Sell insidiously, start early. Don't ever tell your editor you are too lazy to do X or your first book bombed (they'll probably find out the latter, but maybe not).
At some acquisitions meetings, most books are approved. At others, only a few are approved. It will depend on how many gaps there are in the list, how much money is available, and how good the other proposals or manuscripts are. But even in straitened times, publishers have to acquire some books or they will have nothing to publish. Then they cease to be publishers.
There are three possible outcomes from an acquisitions meeting: they take your book (hooray!); they reject your book; they send the editor off to do more work on the book/proposal before deciding one way or the other. Obviously, your favoured outcome is the first. The second means you can go off and sell your book to someone else (let's put a positive spin on this!). The third means you may have to do some more work with the editor.
The need for a book proposal to go to an acquisitions meeting explains some of the delay between you sending your manuscript and getting a contract. Your editor will have to wait until there is an acquisitions meeting with a slot for her to present your book and draft the proposal. Meetings can be cancelled, or run out of time, and then your book may have to wait until the next meeting. It may be bounced back for more work and have to wait for another slot. It's a business, not a personal put-down machine. Don't worry about it. Write something else while you wait.