I have a folder contains a couple of .screen files and an assests folder. I want to open them with WireframeSketcher but I can't find a way to do so. Something like File -> Open -> Go to project and the program opens it.
Use File > Import... > General > Existing Projects into Workspace to import a project into WireframeSketcher. See this article for more details on how projects work: http://wireframesketcher.com/support/faq/best-practices-for-organizing-projects.html