I have read somewhere that we can add supplememt words in meta keywords and it helps to rank our website in SERP,when someone search with the combination of our keyword & supplement words.

For Example:

Keyword: penny stamp
supplement word in meta keyword tag: collection, collecting

It will show our site in SERP, when someone search with query : penny stamp collection.

Is it true?

Meta keywords are not important in search engine aspects. it will not give credits to your website

Hi, little wondering where you get the "supplements" :D
just more give attention for your description than meta keywords.

"Some indexing engines look for META elements that define a comma-separated list of keywords/phrases, or that give a short description. Search engines may present these keywords as the result of a search. The value of the name attribute sought by a search engine is not defined by this specification."

Search engines may index the META Description Tag found in the <head></head> section of your web pages. These indexing search engines may present the content (referred to as a Snippet) of your META Description Tag as the result of a search query.