The slider images on the Responsive Blog theme are coming from the Post.
1. You will first have to create a number of posts and add featured images to it. Also, assign a category to it may be “slider_cat”.
2. Now select the slider category “slider_cat” in Appearance–>Theme option–>Resposnive Blog Homepage–>Slider section
Before that, you will have to enable the custom front page option. You will find the option here: Appearance–>Theme option–>Resposnive Blog Homepage–>Enable Custom Front Page.