How do you find the domain?

Answer 1

The domain of a function, is the range of input values which will give you a real answer.
For example the domain of x+1 would be all real numbers as any number plus 1 will be another real number
The domain of x0.5 would be all positive numbers as the answer to square root of a negative number is not real

Note:
x0.5 means the square root of x

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Not quite. A function is a one-to-one or many-to-one mapping from a set S to a set T (which need not be a different set). A function can be one whose domain is all the cars parked in a street and the range is the second character of their registration number.

A mathematical function can have the complex field as its domain and range, so a real answer is not a necessary requirement for a function.