@sruthilimenzy,

I want a comment form on the homepage 

wpDiscuz comment plugin is designed for single post types (posts, pages, etc…). There is no way to load wpDiscuz comment form on Archive pages like category, tags, author, etc… In case you want to have a comment section on website home, please make sure the home page is a single page, not a list of posts or other archive types. Also, go through all these tips to make sure the comment section is enabled for your home page. Once all is done, navigate to Dashboard > wpDiscuz > Settings > General Settings tab and turn on the “Enable wpDiscuz on Home Page” option.

and have to choose posts from a drop-down menu which lists all posts from the website

We don't follow you. Could you please clarify a bit?