I just want know should I need to define meta keyword tag on every page or just on Index page, Help me I am beginner In SEO
In short, you should make every page unique and appropriate to its content for the best SEO.
This applies to all tags, title, meta, etc. Regarding the actual keywords meta tag, Google does not use this anymore, but many other bots around the internet will use them.
The key is to make sure they are appropriate to the content of the page, and also use them sparingly, only a few keywords.
Google now uses NLP (Natural Language Processing) to understand the content of a site rather than simply look at the keywords as a set of words with no meaning.