Can someone explain the equation for entropy?
Your relation is not correct, so you must not understand something. If I were you I will asked the question in Physics SE but nevermind. 

The good relation is : $$\mathrm{d}S=\frac{\delta Q}{T}$$ 

I let Richard Feynman explain it to you here (when you click on the link wait few seconds)

I hope it will help you, have fun, live long and do chemistry !