Formal:
* Mon nom s'orthographie... (This is the most literal and formal way to say it.)
* L'orthographe de mon nom est... (This is a more formal way to say it, emphasizing the spelling itself.)
Informal:
* Mon nom s'écrit... (This is a more informal way to say it, meaning "my name is written...")
* Je m'appelle... et ça s'écrit... (This means "My name is... and it's spelled...")
Example:
Let's say your name is "Sarah" and you want to tell someone how it's spelled in French. You could say:
* Mon nom s'orthographie S-A-R-A-H.
* L'orthographe de mon nom est S-A-R-A-H.
* Mon nom s'écrit S-A-R-A-H.
* Je m'appelle Sarah, et ça s'écrit S-A-R-A-H.
The best way to say it will depend on the situation and your relationship with the person you're talking to.