Maybe this example will help explain it.
\(\frac{x^5}{x^2}\)
Since x5 = x * x * x * x * x and x2 = x * x .......
\(\frac{x^5}{x^2}=\frac{x\,\cdot\, x\,\cdot\, x\,\cdot\,x\,\cdot\,x}{x\,\cdot\,x}\)
If we take a number, say 5, multiply it by 4, then divide it by 4, we get 5 again. That is...
\(\frac{5\,\cdot\,{\color{green}4}}{{\color{green}4}}\,=\,5 \\~\\ \frac{a\,\cdot\,{\color{green}b}}{{\color{green}b}}\,=\,a\)
So.....
\(\frac{x\,\cdot\, x\,\cdot\, x\,\cdot\,x\,\cdot\,{\color{green}x}}{x\,\cdot\,{\color{green}x}}=\frac{x\,\cdot\,x\,\cdot\,x\,\cdot\,x}{x}\)
We can reduce the fraction by x again.
\(\frac{x\,\cdot\,x\,\cdot\,x\,\cdot\,{\color{green}x}}{{\color{green}x}}\,=\,x\,\cdot\,x\,\cdot\,x\) (When x ≠ 0 .)
And....
\(x\,\cdot\,x\,\cdot\,x\,=\,x^3\)
So, from this we can see that....
\(\frac{x^5}{x^2}\,=\,x^{5-2} \\~\\ \frac{x^a}{x^b}\,=\,x^{a-b} \)
If this doesn't answer your question, can you think of an example problem that would answer it?
Anytime an exponent is confusing, it might help to write out all of the factors. 
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