I'm pretty sure that mean and average both mean(pun not intended) the total value of the data divided by the number of values, giving you an average.
Mode is the value that is repeated most often. For example, if your data set is 1, 3, 4, 2, 2 the mode is 2 because it is repeated twice. If there was another 3, 4, or 1 then the mode would be both values, as they both were repeated the most often.
Hope this helped :)