If you've ever picked up a camera for the first time, it can be incredibly confusing to figure out. Here's some of the basic settings for cameras that you should understand to take photos.
Shutter speed is how much time the shutter takes.
The longer the shutter, the more light gets into the lens
Aperture is how wide the lens is opened during the photo, which also determines how much light gets in the lens.
Higher apertures (which are ironically lower numbers like f/1.8) are used to achieve the blurry backgrounds you see here.
ISO is the sensitivity of the lens to light.
The highest quality photos are taken on the lowest ISO, however there are times when the sensitivity must be raised to accomodate the lack of light.
This is a more in-depth video by Peter McKinnon, a prevalent YouTube photographer.