Change post format

Hi,

I recently added Olsen light and started the customization. I am looking to customize my blog like the demo (at least the post with only the photo). I want to have the picture with the excerpt and the continue button. However, I have the entire post that shows on the main page. I’ve read about using add more tag on a previous post like you’ve suggested but it doesn’t work for me. Do you have another suggestion or perhaps I’m doing it wrong.