Before you learned to read and write you had years of aural training as you listened and imitated those around you. You learned verbal communication before you learned visual communication. It is the same way with music. You have years (some more than others) of music in your mind. The goal is to be able to take what you know aurally and translate that into musical notation. Once you can read and write songs you know, then you can take that knowledge and read unfamiliar music. This all takes practice. Remember that you didn't learn to read overnight, but you probably did learn to read over the course of a year.
Today's lesson will give you a visual representation of some songs in your mind from the last few lessons. Open the pdf for lesson 5 and have it ready to reference as you listen to lesson 5. It would be better if you printed it out so that you could touch the beats as you sing, but you could just look at it on the screen.