This paper is a tutorial intended to give protection engineers a better understanding of how vector matching fundamentals are applied to transformer differential schemes. The need for a concise, methodical approach to vector matching has become evident through numerous lessons learned during substation commissioning. Particular examples of lessons learned from autotransformer standardization projects have created an ideal opportunity for a discussion covering all the essentials and complexities of vector matching fundamentals. The highlights of the tutorial include superimposing the phasor and connection diagrams from the transformer nameplate to illustrate how current flows through distribution power banks and autotransformers when the order of the phase connection sequence is changed. The tutorial also addresses intelligent electronic device (IED) and legacy relaying, grounding sources, and zero-sequence filtering in-depth. A complete understanding of vector matching principles allows engineers to arrive confidently at vector matching solutions for even the most complex transformer topologies. The concepts presented in this paper clearly demonstrate the fundamentals for engineers beginning their career and provide a review for more experienced engineers.