While knowledge and understanding may begin with experiences, they do not originate from experience. So, for example, a logical construction of the real number system is not acceptable. He stopped and stepped on the scales so he could get a weigh. In each case, sketch a rough graph of the function and clearly state the domain and range of the function. Mathematics is a language.
Terminology is important.
As with any language, if you don't read it properly, or if you don't know what the words mean, it can be difficult. A characterization of a function is that it is a set of ordered pairs. The domain of a function is the set of all x values, and the range is the set of all y values. If you think of a function as a rule, then the domain is the set of numbers on which the rule operates, and the range is the set of numbers produced by the rule. Now, this rule can operate on any real number, so the domain of f is the set of real numbers.