Help! Creating a theme is confusing!

[Meltdown]

I have no experience with editing html or php, so I'm left confused on what exactly should I do, so can anyone please answer my questions?

1) I have decided on either Hestia or Fruity as I picked those out of random since there weren't any names on the demos on each image. Anyways there are the style.css, template.html, and theme.php. Which one should I edit to change the colors and such? Do I have to go through the pictures to re-edit them to suit the color theme?

2) How exactly am I suppose to change the div center of certain pictures on the theme without having it go bezerk on me?

3) Is there any possiblity that the themes would be named next time as when the themes were on the demo, it was named by number and not by the actual filename.

[Joachim Müller]

1) style.css, template.html and maybe some graphic resources, depending on the theme.
2) I don't understand the question
3) Again, I don't understand
4) We have a "one question per thread" you agreed to respect when signing up