Regarder means "to look at".
Je regarde la maison. -- I look at the house.Je regarde de belles collines. -- I look at beautiful hills.
It isn't "de" that means "at". The "at" is part of the verb "regarder".
But, strictly speaking, the sentence:
Je regarde des collines is ambiguous. It can mean "I look at hills" as well as "I look from hills".
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