As a preposition:
* Sobre: This is the most common translation and is used in various contexts.
* Example: "Estou falando sobre a guerra." (I am talking about the war.)
As an adverb:
* Cerca de: This is used when referring to an approximate amount or time.
* Example: "Cerca de 100 pessoas compareceram." (About 100 people attended.)
To express an opinion:
* A respeito de: This is used when you want to express your opinion or thoughts on a particular subject.
* Example: "O que você pensa a respeito do novo filme?" (What do you think about the new movie?)
To describe something:
* Em relação a: This is used when you want to describe something in relation to another thing.
* Example: "Em relação ao seu trabalho, você está indo muito bem." (In relation to your work, you are doing very well.)
To ask about something:
* Sobre: This is used when you want to ask about something.
* Example: "O que você sabe sobre o Brasil?" (What do you know about Brazil?)
The best translation for "about" will depend on the context of your sentence.