A struct is a custom data type you define. It groups related variables under one name. You decide what goes inside. Once defined, you create variables of that type just like int or string.
Think of a blueprint. You don't build a house every time. You draw a blueprint once, build houses from it. A struct is the blueprint, each variable is a built house. C++ gives you primitive types like int.
Structs let you build types that match your problem. A Point for coordinates, a Student for grades. You model reality with custom types.