The free account is limited to 2 static pages and two projects. It’s enough to play around and even built a single page website.
Depending on what you want to do (working on unhosted projects and/ or host a website), you will need either an account plan or a hosting plan (or both) to continue. Both do come with more static pages for one website (hosted plans) or for your projects (account plans). Check the pricing lists and details here:
The question on what happens when you cancel your plan with more than two pages has been answered by webflow staff right here: