In the next three segments, we focus on orthogonal functions and their properties, which lead the way into the Fourier Series. In this particular segment, we discuss the inner product of functions and vectors, properties of inner product, orthogonal functions, orthogonal set of functions, the norm, and the square norm of a function. This material is based upon work supported by the National Science Foundation under Grant No. 2019664. Any opinions, findings, and conclusions, or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.