I am new to this

Hey guys I am new to blogging and this theme and I need to know how to edit it !

I want my blog to look kinda like these

http://tinkatollicheats.com/
http://tinkatolliguide.com/

But I don't know even how to change the header !

I want to know how to
1.change the header
2.rounded corners
3.change bacground
4.the side bar titles
5.and coustom navigation bar

BTW try to explain it in a simple way cause I am only 13 thanks