They come from the coefficients in the balanced equation.
For example, in the equation:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
The molar ratios are CO₂:H₂O:C₆H₁₂O₆:O₂ = 6:6:1:6.
We can break this down for any two pairs of compounds.
The molar ratio of CO₂:C₆H₁₂O₆ = 6:1.
The molar ratio of CO₂:O₂ = 6:6
The molar ratio of C₆H₁₂O₆:O₂ = 1:6, etc.