Do you understand the concept all right?
I told a lie. If you can play the guiter, you'll find out my lie. Don't be angry! I told a lie because it was necessary.
I told you that the basic three chords are (C)(F)(G). But "Twinkle, Twinkle Little Star" and others use (C)(F)(G7), instead. In reality, the basic chords are ( C)(F)(G7), not (C)(F)(G). Sorry everybody
The reason? There is no reason. I felt that "G7" was too difficult. Adding the 7th to G makes it difficult. To undertand why, compare G with G7.
These two chords are different. Some guys may say to use G instead of G7 is very different. But the most important thing is that it sounds good to you. For example, guitar cords are often very different from the scorebooks. The ukulele allows you to choose.