Put structs inside other structs. This builds complex types from simpler ones. A Rectangle might contain two Point structs for corners. This is composition, building bigger from smaller.
Example: struct Rectangle { Point topLeft; Point bottomRight; };. Each Rectangle has two Point members. Access with chained dots: rect.topLeft.x. This models real relationships.
A car has an engine, an engine has cylinders. Each level is a struct containing others. Nest as deep as your problem needs.