Answer :

Heiße is when you are talking about yourself, e.g. Ich heiße Rachael.
Hei
ßt is when you are talking about someone else, e.g. Du heißt Ella.

Hei
ße and heißt are different conjugations of the word heißen - the end of the word changes depending on who the word is referring to. Here is the conjugation - 

ich hei
ße - I am called / My name is 
du hei
ßt - You are called / Your name is 
er/sie/es hei
ßt - He/she/it is called / his/her/its name is 
wir hei
ßen - we are called / our name is 
ihr hei
ßt - you (plural) are called / your (plural) name is 
sie heißen - they are called / their name is 
Sie heißen - you (formal) are called / your (formal) name is 

Das and die are different words that show the gender of the noun you are using. There is also a third word, der. 'The' becomes either der, die, or das, depending on the gender of the noun.

Der is masculine e.g. Der Hund 
Die is feminine e.g. Die Katze (die is also used to make something plural)
Das is neuter e.g. Das Hause. 

I hope this helps!




Das is the article for no gender and die is the article for female. Heiße is a conjugation for Ich and heißt also is a conjugation, but for Du.