"Women understand them."
Translation:Ženy je chápou.
The suggested translations are randomly picked by the computer from all possible translations the sentence has. Regardless if the word was taught or not, it is a valid translation and the system has it in order not to turn down correct translations from people who for some reason know that word.
Back to JIM and JE.
CHÁPAT is used with acusativ, so JE
ROZUMĚT is used with dativ, which is JIM
"ně" is used after prepositions, while "je" is used everywhere else. The same is true about other pronouns: ji/ni, jí/ní, jeho/něho etc.
E.g. Vidím ji. (I see her.) but: Mám něco pro ni. (I have something for her.)
Chci je. (I want them.) but: Nemám o ně zájem. (I'm not interested in them.)
"jejím" is a form of the feminine possessive pronoun "její" (her). It can be 1) the locative singular in masculine/neuter gender, 2) the instrumental singular in masculine/neuter gender, 3) the dative plural in any gender.
Here in this sentence, you need "them", that is a form of the pronoun "they". "They" is "oni" in Czech, and we need the dative form to match the "rozumět" verb. The dative form is "jim" (or "nim" after a preposition), as you can see in this table here: https://prirucka.ujc.cas.cz/?id=on&dotaz=oni&ascii=0 (Dative is shown as "3. pád")