Currently, in ghost we create content as post under which there’s post title, featured image, tag, content and some more. I want to know is it possible to add an additional block which can store custom content type and then get that content type to be displayed in a theme?
This will make an additional database column and some more changes in core. So can I know from where should I start to do this?
Hey @Prashant_Verma 
You should check out our tutorial on creating custom collections in Ghost
https://ghost.org/tutorials/creating-content-collections/
From what you’re describing this would suitably provide you with the features you need for a new content type 
I’m not looking for this.
Let me give you an example:
In single post we can grab {{ title }} {{ content }} and some more data. I want to add ratings to each post and grab it using {{ ratings }}
Is this possible in Ghost?
Thanks for providing more information. Going by the name rating does this mean it’ll be vote based or something input by the author? Asking so I can get a better idea of how this will be used 
Yes, author will vote the article.
Also rating is just an example. I am looking to have some more fields.
One way to add a rating system is to use tags, that way you could group items with similar ratings, e.g. all items with 5 star ratings. These could then be displayed together on a single tag page