You might need to be more specific on what you mean by floating window but likely you want to create a surface, then add the info on it - this way you can move the surface (aka your floating window) wherever you want on the screen, or animate it or whatever...
local window = fe.add_surface(640, 360)
local window_bg = window.add_image("images/bg.png", 0, 0, window.width, window.height)
local window_title = window.add_text("[Title]", 0, 0, window.width, 20)
local window_cat = window.add_text("[Category]", 0, 25, window.width, 20)
window.set_pos(100, 100)