An aperitif is a drink one has before a meal. The purpose of the drink is to open up the appetite, hence, the drink will be slightly bitter and tarty. A good aperitif is Campari, a mix which can be combined with anything, like grapefruit juice.
A digestif is a post meal drink, which will aid in digestion. A good digestif is Lustau Cream Sherry. The rich red color and slight sweetness will be a good end to a meal.