How to build collision box with C++?

Hi, I’m new to Unreal engine and I was trying to use link text to build my own meshes dynamically. However, i’m confused with the collision function: It seems that it build collision successfully but how does it make it? I noticed some functions may related to the collision function:

   functions I:
    virtual bool GetPhysicsTriMeshData(struct FTriMeshCollisionData* CollisionData, bool InUseAllTriData) override;
virtual bool ContainsPhysicsTriMeshData(bool InUseAllTriData) const override;
virtual bool WantsNegXTriMesh() override{ return false; }

   functions II:
   FBoxSphereBounds CalcBounds(const FTransform & LocalToWorld) const;
   void UpdateCollision()

Functions I seem to create a collision directly defined by the mesh and functions II seem to create a bounding box.
So, my question is :

   1.How does it define collision? by Functions I or byFunctions II ? or both works in the collison building process?

   2.If i had misunderstood the process, then what's the flow of buiding collision?