Think of / think about, Dream of / dream about

Hi! Would you please explain the difference between “think of / think about” and “dream of / dream about”? Thank you in advance! With kind regards, Oinas.

They are usually interchangeable. You can choose which to use without altering the meaning in any way.

I was thinking of you earlier.
I was thinking about you earlier.

I often dream of flying.
I often dream about flying.