Every single thing around you is made of chemicals. Plants, rocks, computers, food, and you are bunches of chemicals. All chemicals are built with elements, the 109 different symbols on the Periodic Table. Different combinations of elements make different chemicals. Lots of times, chemicals just sit around, but sometimes, when certain chemicals get together, they react.
Chemical reactions take the starting chemicals and end up with new chemicals.
Sometimes chemical reactions are hard to miss. Explosions, burning, color changes, and gas are all good signs that a reaction is going on. Other chemical reactions are less obvious. Changes in temperature, a different smell, or differences in taste are also clues that a chemical reaction is happening. The key is to figure out if you could get back the same chemicals you put in.