Vinegar does different things to different foods. Broadly, it balances flavors by adding a slightly sweet and mostly sour tang, reduces bitterness in a recipe, and enhances the flavor of ingredients in sauces or dishes. It also has specific sweet little uses I bet you'd like to know about. 

When hard-boiling your eggs, adding a teaspoon of vinegar and two teaspoons of salt to boiling water makes the shell come off easily.

When poaching eggs, vinegar helps them set quickly.

When used in a marinade, it tenderizes the meat.

Add a little vinegar to vegetables when boiling or blanching them.

If food becomes too salty, adding little vinegar (or lemon) will cut the saltiness.

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