What do the trend curves and bars in the graph (diagram) show?

In the daily view your activity data is presented in a curve graph. Here you can observe the progress of your measured data over a longer time period. If you tap on a day you can check the hourly summaries of your data for that specific day in a list and in a bar chart.

Your total sleep is also shown in a curve graph in the daily view, where you can compare it over a longer time period.  If you tap on a day/sleep session you can check and compare your specific sleep phases for that sleep session in a list and in a bar chart.

Finally also your daily average pulse is shown in a curve graph in the daily view, for comparison over a longer time period. Here you can also see your highest and your lowest value for each day. If you tap on a day/value, you can check every 10-minute-intervall of that specific day in a list and in a bar chart.