How can we learn the harmony and melody of basic music theory well?

First of all, you should learn science major and minor.

Then change it on the basis of natural timbre.

Harmony major is 6 grades lower.

The melody is turned down by 6 or 7 levels.

The harmony minor reached level 7.

Melody minor is 6 or 7.

You can remember a natural major, a natural minor, a harmony major, a harmony minor, a melody major and a melody minor.

All you have to do is write down one and each of these.

When you meet other keys, you can use the interval relationship between the keys you remember to set those keys.

If the relationship is the same, it is the same tone, and then it is called what tone it starts with.

For example, the relationship between C natural major is: whole tone, whole tone and semitone.

According to this arrangement, you can write D natural major and E natural major. ........

In fact, this method is also suitable for the national model.

This is the way I found it myself.

It is very useful to learn.