"They play with my cat."

Translation: Mereka bermain dengan kucing saya.

[jonafown]

When do we differentiate bersama from dengan?

I mean I get that bermain is a verb and dengan isn't but when does one use one or the other?

[Rick392366]

When do we differentiate bersama from dengan?

dengan = with.
bersama (verb) = bersama-sama = together.

I mean I get that bermain is a verb and dengan isn't but when does one use one or the other?

It can be used like this :

Tini dan Tono berangkat bersama ke sekolah. (Tini and Tono leave for school together.)
Tini dan Tono bermain bersama di pantai. (Tini and Tono play together at the beach.)

Tini berangkat ke sekolah dengan Tono. (Tini leaves for school with Tono.)
Tini bermain dengan Tono di pantai. (Tini plays with Tono at the beach.)

[jonafown]

Ah ok I think I get it now, terima kasih!!!

[mmcaps]

Having read what was said about, I don't understand why this marks "Mereka bermain dengan kucing saya." as right, but "Mereka bermain bersama kucing saya." as wrong.

Is there a mistake here, or is there a grammatical reason that the second one doesn't work?