posts not showing up on default landing page

I am an expert in setting up my W-Site, but have figured out many things along the way. My biggest problem I can not figure out since 3 days. My posts are not showing up on the default landing page and when clicking on the logo. They are visible in the Menue.
I use Yoast WordPress SEO and it tells me “The keyword / phrase does not appear in the URL for this page. If you decide to rename the URL be sure to check the old URL 301 redirects to the new one!”, but I can’t seem to figure out how to fix this. These are probably two separate issues and I would really appreciate help with this.
I don’t have many posts yet and would not mind starting from scratch, but don’t really know how to do that either is i messed up and if it is easier.
Thanks,