Alcohol, also chemically known as ethanol, can bring out the aroma in our meats (see the 1-Minute NomNom "Water you mean I smell?"). It can also improve the taste and smell of our cooking, especially when we cook meats with sauces, juices and marinades.
It does so largely because ethanol is unique: It is both fat and water soluble. It is fat soluble because as a small and organic compound (i.e. carbon related), it can easily pass through the larger organic compounds such as the fat molecules found in meat cells. 
At the same time, ethanol is water soluble. Typically, the carbon in organic compounds makes them hydrophobic i.e. repels water and does not mix. However, ethanol’s carbon chain is short (only two Cs), and the hydrophobic interaction is overcome by its much stronger hydroxyl group (-OH) bonding with water molecules.
The result? Ethanol mixes well with both fat and water soluble compounds in sauces, juices and marinades, which according to Fine Cooking:
- fat-soluble compounds are usually “the flavor compounds in aromatics like garlic, herbs, or other seasonings”, and
- “water-soluble flavor compounds… include sweet, sour, salty, and bitter”.
The alcohol then carries these compounds into our food, giving the food a greater aroma and flavor.
But don't overdo the alcohol. All we need is a small amount of it; if we use too much, it will overpower the aroma and flavor of the food.
photos: in order - depositphotos/Molishka88; Albo73; olla.davies; Kasza; AGphoto