This is the 9121st most frequent Polish word.
swoim
"Swoim" means "one's own" or "to one's own" depending on context.
In this sentence, 'swoim' is used to mean 'my own' and is in the instrumental case, as per the context of having a conversation with someone.
Chciałbym porozmawiać z swoim przyjacielem.
I would like to talk to my friend.
Here, 'swoimi' is in the instrumental plural form, used to indicate the ownership of the items being referred to.
Każdy student musi dbać o swoimi rzeczami.
Each student must take care of their own things.
In this instance, 'swojego' is in the genitive case, showing possession related to the home of Marek.