if this is the result of Tukey-Kramer test for all pairwise comparisons in R

could you please explain for me how to answer this In the table below,please list the four treatment groups in increasing order from the lowest mean to the greatest mean preference score. Then use letter codes to indicate which groups are significantly different from each other. Remember that sets of groups that are not different should share a letter. Groups that fall between two sets and overlap both should have two letters.