Question

how do you do you a combustion reaction?

Answer 1

First you need to define the substances. we'll go with sugar, formula C6H12O6, and burn it in oxygen.\[C_6H_12O_6 +6O_2 --> 6CO_2 + 6H_2O\] and now do math as needed.

Answer 2

for combustion; you need
a fuel; like sugar
some heat ; like a flame
plenty of oxygen