When I can reverse the logical operators? I heard say that is logically equivalent to say it:
$$\neg (p \vee q) = p \land q$$
So every time you have a negation operator in front can make a "distributive" altering the operator from within? And if $\neg(p \vee \neg q)$ then result is $p \land \neg q$? Can anyone give some examples?

Example, as requested...
Suppose I want to know what is the domain of the function
$$
\frac{1}{x^2-4x+3}
$$
That is, I want to find all the $x$ where that denominator is not zero.
So I factor the denominator.  $x^2-4x+3=(x-1)(x-3)$.
When is it zero?  Either $x=1$ or $x=3$.  So when is it nonzero?
$$
\neg\;\big(x=1\;\lor\;x=3\big)
$$
That is, (by the principle explained in Henning's answer)
$$
x\neq 1\;\land \;x\neq 3
$$
In order to belong to the domain, $x$ must be different from $1$ and different from $3$.
