1. Config markdown in sublime text 3

Markdown Editing
Markdown Preview

In sublime: preferences - package control - install package
Input: markdown
Then: choose Markdown Editing, Markdown Preview to install.

2. custom settings of markdown

To change your preferred settings according to the default settings.
custom settings of mardown: 
preferences - Package Settings - Markdown Editing - Markdown GFM Settings - User

3. To use markdown preview in browser

To set markdown highlight.
ctrl + shift + P
Input : ssm (Set Sysntax: Markdown)

To view in browser.
ctrl + shift + P
Input: mp (Markdown Preview: Preview in Markdown)