x11 = window system
responsible for rendering your applications to the to window that it then renders directly to the gpu
awesomewm = window manager
the job of a window manager is to make one window that controls every other window for x. this is responsible for taskbar and alt/tab workspace functionality.
picom = compositor
usually made to complement the window manager, compositors handle more aesthetically oriented parts of the window manager like transparency effects/background blurs, border decorations like drop shadow, animation, and general smoothness