Approval Voting is the simplest multiple preference voting method. The voter just lists the options he/she likes in any order. At the end, the number of preferences for each candidate is counted and displayed in terms of percentages.
Approval method is easy to explain and to grasp, but restricts the voter expressiveness in the sense that he/she has no way to express that he/she likes a candidate more that another, since all listed candidates are considered equally liked. If you have many options to choose from and want to give more freedom to your electors, it is best if you switch to an ordinal voting method.