With funnel reports, you define a specific event path through your game you want your players to follow. For example, Started Game, Visited Store, Purchased an Item. You use the funnel report to see what percentage of your players make it through each part of your funnel and how long it takes for each step.
Player Flow reports allow you to see how players "flow" through your game. For example, what event do players do first? Second? Third? You can follow the event flow of users through the game. You can also "flow" backward and see what is the last event players did. What was the second to last? With this information, you can make changes to improve the experience of your players.