Min, mitt,... deros are the personal pronouns. You probably know this already. There is a simple rule, but I can best explain by example.

First, I'm guessing you understand the genders: 'en and ett-words'

If the object is an 'en' noun, then use min, din, sin respectively

If the object is an 'ett' noun, then use mitt, ditt, sitt respectively

If the object is plural in its possessed form, then use mina, dina, sina as appropriate.

en-form/ ett-form/ plural
my - min/ mitt/ mina
your - din/ ditt/ dina
his - hans/ hans OR sin/ sitt/ sina
her - hennes/ hennes OR sin/ sitt/ sina

our - vår/ vårt /vårra

your - er/ ert/ era

their - deras/ deras OR sin/ sitt/ sina

eg.,

Den är min bil. (It is my car.)

Det är mitt hus (It is my house)

Den är din bil (It is you car)

Det är ditt hus (It is your house)

De är mina bilar (They are my cars)

De är mina hus (They are my houses)

It gets a bit tricky with 3rd Person Singular. If we say, 'Sally drives her car.' Swedish clearly defines if the car belongs to Sally or to someone else. If it belongs to Sally, it's, "Sally kör sin bil." If the car belongs to someone else, it's "Sally kör hennes bil." The same rules apply if it's en, ett, or plural for the sin, sitt, and sina. All the same rules apply also for 3rd Person Plural.

Hope that makes some sort of sense to you. It's quirky to explain it, but it makes better sense once you become familiar with it and/or think it through. If you have questions and/or I made a mistake somewhere in this, please let me know. Best of luck!