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Forget ISO for now.

Think of aperture in your lens like the valve in a water pipe.

Small aperture (big f number), little trickle of water.
Big aperture (small f number), big gush of water.

So this is where you get artistic and I'm afraid there are no rules. Pick your subject of interest. Is it the eyes? Is it the whole person? Is it just the person? Is it the background too?

A wide aperture translates to quite a small depth of field (the region in front of you that appears in focus on your camera) so that might be more suitable if you're interested in a specific detail and want the rest of the photo softer so that the viewer spends their time looking at what you want them to look at.

A smaller aperture translates to a larger depth of field, so more of whats in front of you will be in focus on the camera, so if you have say a couple of people standing at different distances from you, or if you want the viewer to be able to make out the detail of a staircase behind the person, then maybe thats what you're after.

ISO - low ISO lowers the sensitivity of your sensor but makes for smoother pictures. High ISO increases the sensitivity, so you can take fast pics in lower light, but it makes the sensor occasionally choose a tone that's slightly different in different parts of the sensor so the results aren't so smooth.

There are no standard aperture/shutter speed combinations that are "correct" for a photo - you're only going to find out what you like by screwing up and finding out what you don't like. Experiment!