"What will be the difference" can perhaps get complicated with excessive detail, of perhaps limited interest and general use.
But "what situations" is perhaps the most basic principle of beginning photography, the Most Important and Very First Thing we must learn (with regard to using any adjustable camera). If we have not yet learned this, then we absolutely don't know nuthin' about photography yet.
It is well covered many places on the internet, often under the title of "Exposure Triangle" (Google search term). That's not a great name, but it simply refers to the three factors of exposure, which are shutter speed, aperture f/stop, and ISO sensitivity. We do of course need a combination giving proper exposure in the current scene situation, however then many combinations of the three can give the same exposure. We know to pick our choices depending on what the specific scene requires (there is no one general answer).
We would use fast enough shutter speed to stop motion in the scene, to prevent blur. Or maybe sometimes intentionally a slower shutter speed to create a little motion blur. Many scenes involve no motion, in which case we can give preference to one of the other two factors.
We would use a stopped down aperture (towards f/16) to create more depth of field, a larger zone of acceptable focus sharpness. For example, a scenic landscape often needs depth of field extending to infinity, but maybe also back to real close, which is a struggle to achieve. Or some scenes have only minimal depth range, and we can give preference to one of the other two factors.
We might sometimes open the aperture wide (towards f/1.4) to intentionally limit the zone of sharpness (Depth of Field), to intentionally blur the background for example.
The photographer aims for the goal he wants to achieve.
When possible in the situation, we would normally try to use a low ISO for less digital noise in the image. But a low light level might require greater ISO sensitivity to achieve any usable shutter speed or aperture. We would use a high ISO when the lower ISO just wasn't feasible, when it won't otherwise accumulate sufficient exposure. There really isn't any advantage of high ISO for its sake alone.
Proper exposure is selecting the best compromise choice of all three properties, best for the situation in front of the camera at the instant. We use the settings that the scene needs.
The fully automatic compact or phone camera does not require we know anything about photography. Anyone can push the button, and the camera does what it does. The basic exposure might be often OK in an average scene with sufficient light, with no special requirements, but it doesn't take much to exceed the camera's standard solution. The automation can find a choice to get an exposed picture, but it has absolutely no clue about the needs of the specific situation. That's what the photographer learns to do.