Folding means combining ingredients while retaining the air in the mixture. For example, fluffy beaten egg whites, full of the air that has been incorporated during beating, are often folded into batters to lighten them. The Buckwheat Blini, made with the Biscuit Blend, require careful folding to keep them light.
I recommend using a wooden spoon instead of a rubber or plastic spatula to fold egg whites into the other ingredients. When used for folding, spatulas have a tendency to mash or flatten the dough or batter and let the air out of beaten egg whites. Mashed and flattened is not what you want; your goal is to keep the dough light.