The All Player Retention chart will show you how many players have played for a certain number of days across the game's lifespan. These days do not need to be in a row, it could be across a large period (or the whole lifespan of the game). Using the chart below you'll see that over 2000 players have played for one day since logging in one day ago.

All Player Retention Matrix

New Player Retention will show what percentage of players who installed on a specific day have played on the subsequent days.

The first chart allows you to see how many times players are playing, whereas the second one tracks how quickly they are coming back after they've first installed it.