The document discusses relations and functions. A relation pairs elements from two sets, while a function pairs each element from the first set (domain) to only one element in the second set (range). An example is provided of a relation that is not a function because it pairs one element from the domain to two elements in the range. Functions can be represented numerically, algebraically, graphically, or verbally. Evaluating functions involves substituting values into the function formula. A function's domain consists of the valid inputs, while its range consists of the possible outputs.