How du you bend zu sein?

To bend the German verb "sein", you need to conjugate it in the desired tense and person. Here is the conjugation of "sein" in the present tense:

ich bin (I am)

du bist (you are)

er/sie/es ist (he/she/it is)

wir sind (we are)

ihr seid (you are)

sie sind (they are)

For example, if you want to say "you are", you would use the form "du bist".