Subject pronouns and sein
German pronouns are mostly familiar from English, with two twists. (1) The third-person singular has three forms because German has three genders: er = he/it (masc.), sie = she/it (fem.), es = it (neut.). (2) German has THREE words for 'you': du (one friend), ihr (several friends), and Sie (formal — capitalized). The verb sein ('to be') is irregular, just like English 'to be', and you'll memorize it like a chant.
Singular pronouns
ich = I (always lower-case unless starting a sentence — German doesn't capitalize 'I' the way English does). du = you (singular, informal — to one friend, family member, child, or classmate). er = he. sie = she. es = it. Important: er/sie/es also stand in for things, depending on the noun's gender. Der Tisch ist groß. Er ist groß. = 'The table is big. It is big.'
Plural pronouns
wir = we. ihr = you all (informal — talking to several friends). sie = they. The lower-case sie therefore means both 'she' AND 'they' — the verb form tells you which: sie ist = she is; sie sind = they are.
Sie with a capital S — formal you
Sie (always capitalized, even mid-sentence) = formal 'you'. Use it with strangers, older people, in shops, with colleagues you don't know. It's identical in form to plural 'they' (sie sind), so it covers one OR many people politely. Wie heißen Sie? = 'What is your name?' (formal). When in doubt, use Sie — it's never rude.
sein — the chant
Memorize this rhythm: ich bin, du bist, er ist, wir sind, ihr seid, sie sind. Sie sind (formal) is identical to sie sind (they). Practice as: bin, bist, ist, sind, seid, sind.
Examples in context
Ich bin Anna. = I am Anna. Du bist nett. = You are nice. Er ist mein Freund. = He is my friend. Wir sind hier. = We are here. Ihr seid müde. = You all are tired. Sie sind aus Berlin. = They are from Berlin (or — formal — 'You are from Berlin.').
