Most Cameras have loads of different Exposure Modes, each giving you more or less control over how it Exposes your Foto.
Some let you set the Aperture, the Shutter Speed or the ISO. Manual Mode allows you to set all of those Settings to your liking. Actually, it more or less forces you to select all those Settings, because your Camera will not do anything for you. Except for when you use Auto ISO.
Most Cameras also let you know what they think about the Settings you have selected, telling you if you are giving it to much, or to little, light.
And that is pretty much all I know about shooting in Manual Mode. That is because I usually do not use that Mode. Except for when I shoot Video.
I usually shoot in Aperture Priority, and most other Photographers I know do the same. My reasoning for not using Manual is that I still get the Depth of Field I desire in Aperture Priority without having to go through the hassle of selecting the appropriate Shutter Speed.
And usually, I am happy with the Settings my Camera chooses for Shutter Speed and ISO. And for the rare times when I am not, I give my Camera’s Exposure Compensation Dial a quick spin. And in most cases, that is all I need.
When I am shooting Video, everything is different though. That is because my Camera only supports fully Automatic or fully Manual Video Shooting. It still allows Auto ISO though.
And since the Automatic Mode generally chooses to change the Shutter Speed over the ISO, it generally decides on a Shutter Speed that does not Match the Frame Rate. And that Rule where you double your Frame Rate for your Shutter Speed is the only Rule I always follow.
In Photography though, I really do not like Manual Mode. It just takes to much time for how I work.