GC.calloc(), then what?

[Ali Çehreli via Digitalmars-d-learn]

1) After allocating memory by GC.calloc() to place objects on it, what 
else should one do? In what situations does one need to call addRoot() 
or addRange()?

2) Does the answer to the previous question differ for struct objects 
versus class objects?

3) Is there a difference between core.stdc.stdlib.calloc() and 
GC.calloc() in that regard? Which one to use in what situation?

4) Are the random bit patterns in a malloc()'ed memory always a concern 
for false pointers? Does that become a concern after calling addRoot() 
or addRange()? If so, why would anyone ever malloc() instead of always 
calloc()'ing?

Ali