Interpreting graphs is more about guidelines than rules. While graphs are drawn to make relationships and trends in the data clear, this often takes some careful analysis. A sure sign of correct interpretation is being able to put what you see into words.
Draw a graph with time on the horizontal axis and heart rate on the vertical axis to represent this story:
"Alison slept in. Then her alarm woke her up. She jumped out of bed and run to school. Then she sat in boring classes in the moring and exciting math classes in the afternoon"
Draw a graph with time on the horizontal axis and distance on the vertical axis to show how far a car travels every hour for 5 hours if it goes 60 miles per hour.