Ma'am I cannot differentiate b/w substrate and inhibitors

The reactant which is consumed during the enzymatic or catalytic reaction is called the substrate. It converted into a product after the completion of the reaction. For example- Substrates involved in the process of photosynthesis are carbon dioxide and water which are converted into products- glucose and oxygen.

Compounds or agents that combine with an enzyme so as to prevent the normal substrate-enzyme combination and the catalytic reaction or substances that slow down or prevents a particular chemical reaction are called inhibitors. 

A Substrate binds to the active site of the enzyme, and inhibitor either binds to the active site or allosteric site and changes the catalytic activity of enzymes. Both inhibitor and substrate have similar enzyme binding affinities. So it all depends on the concentration of substrate and inhibitor. If the concentration of inhibitor is more, enzyme activity will decrease as the substrate will remain unreacted. Once inhibitor binds, a substrate cannot bind later. An enzyme cannot bind both substrate and inhibitor at the same time.

Hope this clears your doubt.
Regards.