Rebaudioside A is a steviol glycoside pulled from the stevia plant. It provides intense sweetness without calories and does not spike blood glucose.
People stir it into coffee, blend it into smoothies, and bake with it. You can buy it as a powder, liquid, or tablet. Just add it straight to whatever you are making.
The FDA classifies it as GRAS (generally recognized as safe). Some folks notice mild stomach upset with very large amounts. Significant drug interactions are not well documented.