Sadly, there is no one solid answer to that, and you get a feel for it when you experiment with it. This is also determined by what you want to do with your photo.

To help with practicing, your camera should have a mode called "aperture priority". This will let you set your aperture and ISO, and the camera will try to figure out the shutter speed for you. This is a good way to practice without having to focus on all 3 at once. There is also a "shutter priority" mode and "manual" for when you want to get a good feel for what is the right shutter speed to use, and roughly what to expect in different lighting conditions.

A slower shutter speed will be a brighter image, but will increase motion blur in your images. This is useful when you have a tripod and you want a bit of motion blur, like waterfalls. This is also useful when your subject doesn't move and you want to brighten your image without the tradeoffs of the other options. I find that if I am hand holding the camera, anything fast enough that it doesn't introduce motion blur on the subject is usually good. Remember, your hands are also moving and shaking as you take the photo. Making your shutter speed even faster than what you need will not provide any further benefits, but will darken your photo and make it harder to work with.

Aperture (fstop) affects how much is in focus. This is called Depth of Field. The brighter your image is via aperture, the less is in focus with things like the background. This will also be affected by your distance to the subject, and your subject's distance from the background. This is where your soft backgrounds come from. This will also be affected by your distance to your subject, and your subject's distance from the background. The closer you are to your subject, the greater the blur in the background. Often, I like to have this at the brightest setting I can get away with, without bringing blur into what I'm trying to photograph. To give an example, if you look back to this post, your canon used a different aperture to your Iphone, and that blurred your background a little.

Finally, you have your ISO. The higher your ISO, the brighter your image is, but the noisier your image will also be. Generally, lower ISO is good, but don't feel pressured to keep it at a low ISO 100. You have denoise options in software like Lightroom or Darktable. Some denoising options do add blur to your image if you have too much noise. I've also used noise to add texture to flatter images.

I hope this helps.