– Καλά, ευχαριστώ. Εσύ;
– Κι εγώ καλά.
– Fine, thank you. You?
– I’m fine, too.
This dialogue is informal. Both people use the singular “you” (εσύ). The verb is also in the singular.
– Καλά, ευχαριστώ. Εσείς;
– Fine, thank you. You?
Both people use the plural “you” (εσείς). The verb is in plural.
This dialogue can be formal when speaking to one person.
This dialogue can be formal or informal when speaking to more than one person.