firma

/firma/

Cases

SingularPluralWhen to use it
nominativefirmathe firmfirmalathe firmsthe plain dictionary form — the doer of the sentence
genitivefirmanıthe firm'sfirmalanıthe firms'the owner — whose it is
accusativefirmanıthe firm (as the object)firmalanıthe firms (as the object)a specific, known object — whom or what
dativefirmağato the firmfirmalağato the firmsdirection or recipient — to where, to whom
locativefirmadaat / in the firmfirmaladaat / in the firmswhere it is; also having — mende bar, "I have it"
ablativefirmadanfrom the firmfirmaladanfrom the firmswhere it comes from; also "than" when comparing
When to use each case
nominative
the plain dictionary form — the doer of the sentence
genitive
the owner — whose it is
accusative
a specific, known object — whom or what
dative
direction or recipient — to where, to whom
locative
where it is; also having — mende bar, "I have it"
ablative
where it comes from; also "than" when comparing

The endings are the same ones the pronouns wear — that page explains when each case is used.

With an owner

One ownedSeveral owned
myfirmammy firmfirmalarımmy firms
yourfirmangyour firmfirmalarıngyour firms
his / herfirmasıhis / her firmfirmalarıhis / her firms
ourfirmabızour firmfirmalarıbızour firms
you all'sfirmağızyou all's firmfirmalarığızyou all's firms
theirfirmalarıtheir firmfirmalarıtheir firms

The overlap in the last rows is real, not a mistake: firmaları can mean "his / her firms", "their firm", or "their firms" — context decides.