Just because your child will be playing fun online games doesn't mean the same value won't be there. Create a comfortable study zone. Turn off outside distractions such as cell phones, radios or TVs.
Book knowledge is the ability to recognize book formats and purpose. Early readers learn how to hold a book properly, to read English from left to right, how pictures supplement the story, and that books have basic components such as a front and back, spine, pages, covers, and more. Children automatically learn these things at a conceptual level long before they understand the purpose of each component.
A comprehensive set of worksheets covering a variety of subjects can be used to expand your child's learning experience. A worksheet about shapes can be used as part of a game to find shapes around the house, counting worksheets can be used to count things you see in the grocery store and so on.
While there are many preschool worksheets available, some are more useful than others in terms of versatility. There is a lot more to school readiness that just knowing the alphabet and counting to ten.