• Vectors both 3D and 4D, and what the W component should be set to
• Left-hand and right-hand coordinate systems, and which one your game is
• The dot product, and what it's useful for
• The cross product, and what it's useful for
• Matrices, how they represent orientation and position and how you can combine them
• Quaternions

Even if you're not The Graphics Guy, you're going to use vectors and vector maths 80% of the time. They're the onions of our fun bolognese.