They are conjugations of the irregular verb "sein" which means "to be" in German.

ich bin - first person singular "I am"

du bist - second person singular "you are" (note: this form is used with family or friends, it is informal and not used with strangers)

er/sie/es ist  - third person singular "he/she/it is"

wir sind  - first person plural "we are"

ihr seid - second person plural "you are" (again, this is informal)

sie/Sie sind - third person plural "they/you are" (Sie is the formal "you" and is used to address people that you do not know very well.

http://www.dw.com/en/learn-german/s-2469

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gramer example ; ich bin = I'am / Du bist = you are / wir sind,sie sind we..vs