Where sample method is called in UVM RAL.!

Hello all,
In this Coding Guideline: Wrap covergroups within uvm_objects(Registers/FunctionalCoverage | Verification Academy), there is a “covergroup_wrapper” class which contains covergroups and sample methods.
My doubt is
1)when and where should this “covergroup_wrapper” class be created and
2)when to call the sample method of covergroup_wrapper class?