Forget the fancy stars in the image oo.
The image above is called “Circle of 5ths” when moving in clockwise direction and “Circle of 4ths” when moving anti-clockwisely.
It would help you to remember many key things in music but here I will only tell you how it helps you build your interval knowledge of perfect 5ths and 4ths.
From C to G is a fifth while going backward from G to C on this circle is a fourth interval.
Another instance,from F# to Db is a fifth while backward from Db to F# is a fourth.
It’s the same thing counting two and half tones for 4th interval while counting three and half tones for 5th interval but this clock or circle will help you to remember easily without counting anything.
Just look at it like a multiplication table that you use when you want to solve simple mathematics.