Your name is in German

Answer 1

In English, nationalities are normally attributed to people as adjectives, e.g. I am English rather than I am an Englishman. The Germans don't use nationalities as adjectives when referring to people directly, they use nouns. They literally say I am (a) German, I am (an) American, I am (an) Englishman:

Ich bin Deutscher. (not the adjective deutsch)

Ich bin Amerikaner. (not ich bin amerikanish)

Ich bin Engländer. (not ich bin englisch)

There is no requirement to to use ein (a) because it is a direct attribute as in er ist Fußballer - he's a football player, sie ist Schriftstellerin - she is a writer.

Therefore:

You are German. - Du bist Deutsche/Deutscher. (female/male, informal)

You are German. - Sie sind Deutsche/ Deutscher. (female/male, formal)

n.b.

The adjectival form is used in German when the nationality is linked to another noun:

Er ist amerikanischer Saatsbürger. - He's an American citizen.

In such cases the nationality is linked to the object (Staatsbürger and not the subject er, and therefore assumes the adjectival form).

Answer 2

Wie heisst du?
Wie heissen Sie?