Matter is not created or destroyed.
6H2O + 6CO2 ------------> C6H12O6 + 6O2
This is the balanced form of the equation. 6 water molecules + 6 carbon dioxide molecules equals 1 glucose molecule and 6 oxygen molecules.
All atoms must match on both sides to meet the conservation of matter. If you add up the totals on each side you get:
12 Hydrogen
|
12 Hydrogen
|
18 Oxygen
|
18 Oxygen
|
6 Carbon
|
6 Carbon
|
Matter is conserved through the reaction.