Differs widely from company to company. Identifying and brainstorming new products, talking with users and potential users, figuring out if the product makes f

Differs widely from company to company. Identifying and brainstorming new products, talking with users and potential users, figuring out if the product makes financial sense, writing up requirements (with widely varying levels of detail), working with developers to ensure the product being built matches the requirements, keeping people across the company informed about the product's status with the appropriate level of detail, describing the product to and then training sales, coming up with longer-term plans (the 'product roadmap'), creating marketing materials for the product, chatting with the media about the product -- I've done all of those things as a product manager at a variety of places. Product managers become useful when a company grows, people specialize their functions somewhat, and everyone no longer knows everything about what everyone else is doing. Good product managers do their best to eliminate surprises. It's the sort of job where you learn by doing, and in my experience there's a lot of terrible product managers out there.