@burcinc-- E stands for enzyme and S stands for substrate. When a substrate (molecule which the enzyme breaks down) attaches to an enzyme, it is called the enzyme-substrate complex, or ES.
So you know that competitive inhibition is when an inhibitor binds itself to the same place on both the enzyme (E) and the substrate (S) and noncompetitive inhibition is when the inhibitor binds to the enzyme (E) and also the enzyme-substrate complex (ES), right?
Uncompetitive inhibition is when the inhibitor binds only to the enzyme-substrate complex (ES) and anywhere it wants on it.
The names actually give you a hint about what is going on. In the first one, competitive inhibition, there is a competition both between the enzymes and the substrates for the inhibitor. Because the inhibitor will only bind to a free enzyme and a substrate that has the same shape as the inhibitor.
When it is noncompetitive, the inhibitor is fine with binding to a free or "unfree" enzyme (enzyme with a molecule already binded to it), so there is no competition in that sense. Although the substrates must still have the same shape as the inhibitor.
When it is uncompetitive, there is absolutely no competition whatsoever. The substrate can be in any shape for the inhibitor to bind to it and it will directly go for the complex and not require any free enzymes.
I think this will help you to understand a little better. Good luck!