GLFW creates windows, handles input, manages multiple monitors, initializes different OpenGL implementations and even Vulkan, so it's a library that provides different functionality for different platforms.
GLFW uses the Win32 API underneath on Windows, so everything GLFW gives you it's attainable by using Win32 alone.
It's your decision whether to go the Win32 route or the library route. Do you want to have full control on the platform layer? Use Win32. Do you prefer working on graphics and OpenGL and don't care that much about how you get a window, context and the input? Use GLFW to get started. You can always switch to Win32 in the future.