The app has support for tracking night sleep and naps with separate statistics and charts.

To keep it simple you track both naps and night sleep using the Sleep activity and depending on the time of day of the sleep the app will count the nap as either night sleep or a daytime nap. You may adjust the normal bedtime and wake up times of you baby under the Settings screen, however the times don't have to be exact if you baby is not on a schedule yet. The app will figure things out correctly. You can also turn off this feature under Settings if you just want to track naps (more useful for newborns).