How does Google know what post your referring to in your backlink?

Newbie question: If your WP site is showing a particular post on your homepage all the time, IE via plugin called postmash or other method, and you create a backlink for SEO purposes, IE, in an article, what type of link should you use in your backlink: https://www.dogfood.com or https://www.dogfood.com/dog-food/? Note, when I click on my right sidebar under recent posts for the particular post the address bar will show https://www.dogfood.com/dog-food/. If I click on the H1 header it will show https://www.dogfood.com.

Now I don’t like the latter, https://www.dogfood.com/dog-food/ because it seems that would lesson the SEO effectiveness being I am trying to rank for https://www.dogfood.com and the actual post I have appearing on the home page.

So what do most people do when they want their whole site really to target one particular post? Do they have the post they are really trying to rank for always appear on top using a plugin or other method?

What I’m confused about is with multiple posts on the homepage how does the Google crawler know what post your referring to? Suppose https://www.dogfood.com shows 5 post with the first post being the one I actually want to rank for. How does the Google crawler know which post I’m actually referring to?

Now, if I have only one particular post the one I want to rank for show up on the homepage via plugin, IE, Postmash, will Google actually see the correct post and not another? In other words, is Postmash just showing the post to the user and the actual hard code is showing google crawler a different post? Hope that makes sense.