सः means he, that (masculine)
सा means she, that (feminine)
तत् means that (neuter)

Even for non-living things सः, सा are used. Same way तत् is used for living beings too.
These can be used only in singular (एकवचनम्)

सः पुरूषः – He is a man
सः युवकः – He is a youth
सः बालकः – He is a boy
सः गायकः – He is a singer
सः कृष्णः – He is Krishna
सः चषकः – This is a cup
सः आसन्दः – This is a chair
सा माता – She is a mother.
सा भगिनी – She is a sister.
सा महिला – She is a woman.
सा सीता – She is Seeta.
सा लेखनी – This is a pen
सा दूरवाणी – This is a mobile phone.
सा घटी – This is a clock.
तत् पुस्तकम् – It is a book.
तत् फलम् – It is a fruit.
तत् पुष्पम् – It is a flower
तत् पर्णम् – It is a leaf.
तत् मित्रम् – It is friend