Reactants are listed on the left or right side of an equation

They are listed on the left side of an equation. Assuming you're talking about chemistry.

This is the arrow production of products in basic chemistry equations.

Reactants - - > Products

In later chemistry, there would be equilibrium equations in chemistry, meaning both sides are reactants and both sides and products.

Reactants - - - > Products

Products < - - - Reactants