Disulfide bonds form between different amino acids of a protein chain and the help to stabilize and maintain a distinct three dimensional form. In principle this looks like this (pipcture from the Wikipedia page on Disulfide bonds):
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Disulphide bonds (or bridges) can also hold different subunits of larger protein complexes together, one example for this would be antibodies. Here the light and the heavy chains are connected by disulfide bonds, they also play a role for maintaining the structure of the single protein chains (image from here):
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