ders

/ ders /

Cases

SingularPluralWhen to use it
nominative ders the lesson dersle the lessons the plain dictionary form — the doer of the sentence
genitive dersni the lesson's dersleni the lessons' the owner — whose it is
accusative dersni the lesson (as the object) dersleni the lessons (as the object) a specific, known object — whom or what
dative dersge to the lesson derslege to the lessons direction or recipient — to where, to whom
locative dersde at / in the lesson derslede at / in the lessons where it is; also having — mende bar, "I have it"
ablative dersden from the lesson dersleden from the lessons 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
my dersim my lesson derslerim my lessons
your dersiŋ your lesson dersleriŋ your lessons
his / her dersi his / her lesson dersleri his / her lessons
our dersibiz our lesson dersleribiz our lessons
you all's dersigiz you all's lesson derslerigiz you all's lessons
their dersleri their lesson dersleri their lessons

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