New to GetSimple: how to change Title text?

[elpepe]

Hi, I've already installed GetSimple without problems, chosen Cardinal theme and now I want to change the title of the home page. I noticed that the theme get that with a function get_site_name(). I want to put my logo here and I don't know how to make it. Additionally, to change the elements background colors the straight way is changing their properties in the .css file? If it is so, how can I proceed to keep the original colors and generate the new css as a new template? It may seems I didn't understand nothing but I found very cumbersome if no existent guides to make this things.
Thanks in advance and best regards.