お is not a particle, it's an honorific prefix before certain words. E.g. お水 (o-mizu) "water", お名前 (o-namae) "name". Basically, it makes the phrase sound more polite and is often used in questions or requests. を is indeed a particle, which marks a direct object in the sentence (i.e. the object at which the action is aimed). 私はりんごを食べます (watashi wa ringo o tabemasu) = "I eat an apple". ("eat" is the action; "apple" is the direct object) 私は本を読みます (watashi wa hon o yomimasu) = "I read a book". ("read" is the action; "book" is the direct object)

お doesn't exist as a particle. を (pronounced as "o") marks the object of a sentence.

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