Backlinking should be done to Home page or to the page or to the post??

[bloggytalky]

I am Learning SEO these days and I am confused about backlinking here are the questions

1.) if I want to rank a keyword with 80+ difficulty and suggested backlinks are 800+ then do i need to give 800+ domain link to a key word or any domain nos. and +800 backlinks?
2.) where should I need to give backlink if post contains keyword and post is in category
a.) Homepage b.) page or category c.) post containing keyword
3.) if I give most of the link to my cornerstone page which contains internal links to 15 blog posts then it is beneficial or should i give back links to all 15 posts individually.

Kindly help me I need your help to check here is my homepage and cornerstone page and article post kindly go through it and give me proper suggestions.

MAKING A BLOG- Cornerstone page