Most camera manuals do not provide enough information on mode settings.

If people use modes more often they will get better photographs.

Modes are used to adjust the camera for the best settings for special or unusual situations.

Modes are a way to provide manual controls to a camera that does not have manual controls.

Most of the time you should shoot in Auto mode.
But when you have a mode setting that covers a situation that you sure to use the mode.

Cameras makers do not tell us what settings are being effected by a certain mode. They use settings that an experienced photographer would use under those conditions.
Here is my best guess for Portrait mode:
Set the camera:
to the best detail setting (megapixels and .jpg quality)
to the brightest aperture (f-stop).
to an ISO setting that will permit a shutter speed of at least 1/60th of a second.

I can't outguess the camera maker on his choices for a mode, but if the name of the mode fits the situation.....use it.
If there is snow on the ground...use Snow mode.
If you are at the beach...use Beach mode
If you are photographing fireworks...use fireworks mode.
....but also use a tripod because the fireworks mode will select a slow shutter speed.
If you are shooting action..use a setting that implies movement, such as sports mode.
etc, etc.