If you're using Genesis, it's actually great start point! Themes should be modified via child themes, so take a look at this - it's pretty easy:

Building Child Themes - Genesis Framework
Child Themes « WordPress Codex

Now, to change colors - you need to learn CSS. To change structure, you need to learn HTML.

HTML Tutorial
CSS Tutorial

This is to get you started, if you find it easier - you may look for HTML & CSS videos on youtube. There's plenty of it. Good luck!

You need to learn some coding languages to do the above task. If you are new to coding then you need to learn html and css first . Wordpress have dynamic website for this you must learn PHP. For php tutorial see php.net . This is the best website for beginner level to advance level.

You need to be able to read and write html and css, and basic understanding of php would help too, but for simple modifications it's enough to globally understand the php you are reading without being able to program it your self.