The major difference between the 2, is that actual yield is the amount or quantity of something, some substance and or product that you actually obtain upon working on the experiment, and or running a reaction. The theoretical yield, is the supposed amount and or quantity of product that you should obtain assuming that the reaction occurred perfectly and all of the reactants have been converted to products.
Usually the actual yield would be less than that of the theoretical yield, indicating that a chemical reaction and or process will never produce the complete or full amount of substance of what you supposed.
