Uncertainty of how it all works is my opinion. Like how is it installed. What is making a partition and what are these warnings? What happens to all my pictures

Uncertainty of how it all works is my opinion. Like how is it installed. What is making a partition and what are these warnings? What happens to all my pictures and documents? What distro is best? Do I lose all my paid for software? How do I now do all the things I am used to doing? I remember the first time I partitioned my hard drive and did a dual boot and I was really unsure about so many things. It is intimating.