In a chemical change, a substance is altered both chemically and physically. They will display different physical and chemical properties. To be able to spot all chemical changes, you will have to build an understanding of the world around you and how substances react. We will do this in-dept later in this course as we study chemical reactions. Again, here having an idea of some key words to look for can help. Substances that react, burn, or decompose are experiencing changes in their chemical properties. For example, glucose (C6H12O6) undergoes metabolism to form pyruvate (C3H4O3), as part of our body's metabolism of food to provide energy to the cells. Chemists would write this process as (leaving out some details):
C6H12O6 --> C3H4O3
Notice how, unlike the example with water, the substances on each side of the reaction arrow is not the same. The two sides have some similarities, like having C's, H's, and O's (carbon, hydrogen, and oxygen atoms), but their number have changed (those numbers seen following the letter and below the line of the text).
Here's a video explaining what happens when the chemical and physical properties of substances change, summarizing what was said above.