Combine results and produce a final tally

Hello,
First, let me say I am brand new to excel. This is the problem that has been given to me. I have two lists of the activities of my reps. One is for their "buy" activities and the other is for their "sale" activities. I want to produce one list that gives me the total of each rep's buy and sell activities. I have been able to combine the lists and sort the names so that duplicate names are in order but I don't know how to write a formula or if such a formual is possible, that can check all the names in the list and when duplicates are found the values are added together and posted in a new column.

Thank you in advance for any help you can provide.

dja