When a person is spelling a name, there are several rules that apply:
The spelling looks exactly as the name looks when simply typed.
…My name is James Edwards, J-a-m-e-s E-d-w-a-r-d-s.
Leave spaces where there are spaces in the name.
…My name is Mark Van Meter, V-a-n M-e-t-e-r.
If someone says “cap” or “capped,” there are two choices:
…My name is McDonald, M-c-D-o-n-a-l-d.
…My name is McDonald, M-c-cap D-o-n-a-l-d.
If someone says “double…,” there are two choices:
…My name is Miller, M-i-l-l-e-r.
…My name is Miller, M-i-double l-e-r.