Firstly, have you even created a blog?
you have to create one, choose a desireable blogskin, click "download blogger main"
copy the code, go to "layout" ,"edit template"(if yours is in the new version)
then paste the code in the white box.

after you paste it there, scroll down and click save template.
next, scroll really really down until u cant scroll anymore
and click"revert to classic template".