In order to find the zeros of the function, it is necessary to equate the right side to zero and solve the resulting equation. Suppose you are given a function f(x)=x-5.
To find the zeros of this function, we equate the right side to zero: x-5=0.
Solving this equation will get x=5 and this value argument and is null function. That is, when the value of argument 5, the function f(x) vanishes.
When finding roots of an equation may be extra roots. It is easy to check: simply substitute the obtained value of the argument to the function and verify whether the function to zero.
Sometimes the function can not be expressed in explicit form using your argument, then you just need to know what is this function. An example of this is the equation of the circle.