What do board game publishers do? What are the difference between them?
I'm satisfied, from the discussion in the comments, that this question is off-topic.
It seems like a perfectly answerable question, and would invite a broader scope of questions around board game design and publishing.
Your question is vague and doesn't state a specific problem. Questions that ask for general knowledge (could be reframed as "I'd like to know XXX") are often too broad and can be closed for that reason. If it takes a book to properly answer, this isn't the place.
The question also demonstrates very little investigation on your part. A brief googling gave me tons of information. Most of the boardgames I've backed on Kickstarter contain updates with a lot of information from the designers & publishers. You may have some of this knowledge, but your question doesn't convey that.
If you demonstrate that you've done some initial research and focus your question on clarifying something that still confuses you, your odds of getting a good answer go up.
It's also possible that you have a distinct problem in mind and believe that knowing more about game publishers is the missing piece you need to solve it. It's better to lead with the actual problem you are facing, we can then focus on helping you directly instead of trying to answer vague questions that probably won't give you the full answers you seek.
Some examples:
I don't necessarily see the problem with your question. It's only a broad question if you go into every detail, which is not necessary to provide you with a useful answer.
The sad part about the answer is that a lot of the differences between publishers are based entirely on choice.
In the end, a publisher is just a brand that puts a name on a line of products so they have more leverage in the market. Whether or not they make or buy their pieces, make or buy their game concepts, and which terms and conditions they use for their partners, all depend on the choices they make.
