Descartes doesn't actually believe that there is an evil demon out there, he rather considers whether there is any evidence which would enable him to prove that there is not one. The 'evil demon' hypothesis is just one way to call into question the justification of beliefs which are derived from deception and hence his hypothesis is a potential hazard for many of the things we think we know. The point is to sift among our beliefs to find those that are more securely justified than others. Having considered the existence and aim of such a hypothesis, I will now begin to illustrate my opinion, using a similar methodology to Descartes himself. When I see a clock, I assume that it was created by man.
Man is a term referring to our species.
Similarly, when I see my friend sitting across the room, I suppose that he is a real person who has life and is aware of his surroundings through the use of his senses. I believe that his life and senses and awareness are similar to mine, since he is the same species as me. If I speak his name, he hears me and knows I have addressed him. If I ask him the time, he subjectively sees and hears the clock in a similar manner as I do. If I sing the words of a song, he hears the words and recognises the song.