In order to understand the chords completely, you need to study certain music theories. It is recommended that you try to read some technical books about the system of chords.
Don’t worry! This page is for people who don’t want to read those books.
From now on, when you see chords, please remember these "Three Rooms."
First, there should be a note from A to G in The Yellow Room. Sometimes, "#" or "♭" may be added, but The Yellow Room will never be vacant.
Other rooms may or may not be vacant.
To avoid confusion, we are going to skip some things for now.
As you can see in this picture, on the left side of the vertical line (The Yellow Room and The Red Room) are necessary information.
On the right side, the remaining one (The Gray Room) is not as important and we will go into details later.
It will be fine as long as you understand The Yellow Room and The Red Room.
Based on this picture, we need to understand which symbol have to be followed or ignored.