Understanding basic example

Handle(AIS_Shape) is a smart-pointer to AIS_Shape (holding a raw pointer to AIS_Shape as a class field). The main purpose of smart-pointer is to delete the object once it is no used anymore and hence to avoid memory leaks. Object lifetime is managed by reference counter stored inside the object, incremented with each new copy of Handle(AIS_Shape) and decremented with each destruction of Handle(AIS_Shape) when it goes out of scope. Handle(T) is a preprocessor macros expanded to opencascade::handle<T> template class. It is similar to std::shared_ptr<T> template class from STL with some differences.

When you write

Handle(AIS_Shape) aShapePrs = new AIS_Shape (aShape);

It can be expanded as (without compiler optimizations):

AIS_Shape* aShapePrsPtr = new AIS_Shape (aShape);
Handle(AIS_Shape) aShapePrs;
aShapePrs = aShapePrsPtr;

This works because Handle(AIS_Shape) class defines an assignment operator operator=(AIS_Shape*) capturing raw pointer into smart pointer. Note that in some other frameworks implementing smart pointers such assignment operator from raw pointer is considered dangerous (potential memory leaks / memory corruption on misuse) and disallowed, so that the only way to create smart pointer there is to pass it to smart pointer constructor or to dedicated method reset(T*). But Handle(T) has no such restriction due to slightly different design and usage approach, so that it could be initialized in both ways.