I've been making errors on Duolingo, and reading up on grammar. I still don't have a firm grasp on what I am getting wrong. Some sample sentences :

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a) Me dirá los secretos si no se los digo a nadie. (I don't really get why there is a "se" and "a"...the first part of the sentence I can understand. Do we use se because him? And we use a because it's directed to someone else?)

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b) Aquí tengo la aspiradora, ¿ (te la) doy para limpiar el piso del cuarto? (The "te la" in brackets is what I got wrong...that's the "give to you" part?)

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c) Las sillas no le gustaron, así que me las devuelve. (So the "que" becomes the subject of the sentence (chairs) but why is it las devuelve? I get confused where I need to use el/la/las in the second part of the sentence)

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d) Las máquinas de esta compañía son silenciosas. (I understand this if "de" is "of" which is one use of it?)

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Él quiere quedarse con ese abrigo, así que lo va a comprar. (Once again I get the first part of the sentence, but not the "lo va a comprar" I get confused whenever it's "va a")

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I know Spanish is Spanish and so I can't use the English grammatical order one for one, I am just trying to understand it better. Thanks, everyone for their help.