Subtly, through a lot of different, often very small things.
When a group of boys harasses or bullies a girl out of joining the computer class/robot club/science club/whatever, because society has told them that computers, robots, and science are "boy" things, so they feel justified in policing "their" territory? Patriarchy at work.
When a couple has a baby, and decides that the mom should be the one to take off work to care for it, even if she has a better job and/or less interest in being a parent than the dad, because he doesn't want the "embarrassment" of being a househusband? Again, patriarchy.
Every little girl who has gotten a doll instead of the truck she really wanted, and every little boy who has gotten a truck instead of the doll he really wanted, because dolls are "girl" toys and trucks are "boy" toys, is a victim of patriarchy.
And it's not just women who are victims of patriarchy.
Every man who committed suicide because getting help was too "womanly", every man who worked himself to death because he had to be a "good provider", even if he could have "provided" just fine without working so hard, every little boy bullied or shamed because he was a "sissy", is a victim of patriarchy.