You are reading the documentation for an older Pickit release. Documentation for the latest release (3.2) can be found here.
Pickit has two general detection engines, each optimized for a different type of shape.
Teach is the most versatile engine, and well suited for most shapes of known fixed sizes, both simple and complex. It is the recommended detection engine for most applications, ranging from complex shapes to cylinders of known dimensions.
Flex is meant for detecting simple geometric shapes in 3D (cylinders and spheres) and 2D (squares, rectangles, circles and ellipses). It can detect instances of the same shape with similar or different sizes. It is recommended for cylinders of varying sizes, but for cylinders of fixed sizes prefer Teach.
You can learn about the main ideas behind the Teach engine by watching this video tutorial.
Pickit also offers detection engines optimized for specific part shapes and arrangements:
Bags, which is specially designed for detecting bags on a pallet.
Pattern, which is similar to Flex. It looks for 2D shapes (rectangles, squares, circles and ellipses) of known fixed size, and is especially useful for detecting parts that are aligned and touching.