You're going to have to elaborate a little. Are the calipers moving when you operate the levers? Are the pads all present and correct and not loose in the calipers? Do the pads correctly make contact with the rim when you operate the levers? Is it a 2nd hand bike?
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That's about as much help as I can be, given the information you've provided.
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A pic of the caliper would be useful.
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