How do you find a domain of a function

I’m not sure what this is in reference to,
but,
If the domain is all real numbers , a function with a fraction that contains a variable in the denominator , you would want to set the bottom equal to zero and exclude the x value, then solve for the equation.

if you’re finding the domain and range in calculus ;
domain being D = (all possible) x values
R= y values. domain all real numbers , Y is not going to be all number because in y=x^2, only positive numbers on a graph no way to have negative numbers,

the range is always going to be greater than of equal to zero.

you can do this by : looking at the graph, or by solving the problem algebraically looking at y=x^2 (x^2 is NEVER going to be negative)
so the range (y-values) are always going to be zero or greater than zero, you can plug in any number for the range for x and it’s still going to be able to square it.