There isn't a big difference and you can usually use either "of" or "about". However, my feeling as a native speaker is that "dream about" is more likely to be used when describing dreams you have when you were sleeping and "dream of" is more likely to be used when describing something or someone you think about a lot, not necessarily when you are sleeping. For example: "I often dream about strange things at night" "I dream of one day giving up work and travelling around the world"

'Dream about' is used for an actual dream eg I dreamt about an old schoolfriend last night. 'Dream of' is used for an ambition or fantasy eg 'I dream of sailing round the world one day'.

To dream of something implies a want, a need, a desire: I dream of traveling the world I dream of world peace I dream of Wayne To dream about something is to literally dream about something, and it's usually presented in the past tense: I dreamt about winning the lottery I dreamt about flying I dreamt about being a millionaire To use it in the present tense is more passive.

well i don't see that there's a big difference between dream of or dream about but as my teacher say it's more suitable to use dream about

Think of- that it is your chief focus, it is hold in your mind. Think about- less intense focus.