You can also add items to the Tournament History.
The Tournament History is sort of a running log of everything (mostly) that happens during a tournament, including what time rounds change, or if you undo an action, etc.
The Action Summary on the Summary tab is simply a listing of all of the important actions that occurred during the tournament, like buy-ins, rebuys, and bust-outs.
As an example: you buy-in player A, realize this is the incorrect player to buy-in, undo the buy-in for player A and then buy-in player B.
The Tournament History will show that you bought-in player A, then undid the buy-in of player A, then bought-in player B.
The Action Summary will only show the buy-in of player B. As far as the tournament is concerned, player A was never part of the tournament.
I've added an item to the to-do list to be able to include user-created Tournament History items in the Action Summary.