WP beginner, question about custom theme

So im trying to get used to this whole CMS thingy, especially wordpress. Before i have been doing everything from scratch, like html CSS and simple php. I dont want to jump in and stir around in a css file of an already existing theme, pretty much takes out the fun of making a site IMO.

So my question is… i have got all this parent templates like, home.php for example, and if i choose to write something on the home page via wordpress-pages the text just sits there at the top of course.
But if i want to edit the text in one of the divs, say i have a two column section, and i want to edit the left div, how do i do this? Do i have to create a child template to the home.php theme and target the div or how would it work?

Hope u get what i mean my english isnt perfect=)

thanks beforehand