Hello, I'm very new to guitar playing, but am very motivated at this point (31 years old and practicing a LOT!). I've been working through the lessons here, but one thing I'm confused about is the difference between playing a song with just strumming chords, and actually playing the notes.

For example, I have a book (4 chords songs) with "Wonderful Tonight" in it. It gives the 4 cords to use and shows rhythm slashes for strumming these chords through the whole song. It also has the notes and words bellow that. Now, when Clapton plays this song, he isn't strumming; he's playing notes. I don't understand when is the best time to play notes vs. strumming chords? I also notice people hold cords but pick single notes while holding that chord. I guess I'm very confused -- please set me straight.

thanks,
Jeremy