I want to know about the method used for deciding the contribution

How contribution is calculated has not been publicly disclosed. But it is calculated from the scores of your comments and blogs. Newer comments and blogs are more valuable. Also it's known that the higher your contribution is, the harder it is to get more.

How to make the contribution in codeforces positive

Your contribution is negative because you have posted useless comments. For example, this comment was posted under a blog that is 10 years old, despite the popup that comes up when you comment under there that tells you to not do that. If you just want to say "thank you", leave an upvote. Writing "thanks for the info" under a blog or comment pollutes the comment section and Recent Actions.

Similarly, for many people a comment like this is basically spam.

And this blog? Because there have been tons of similar blogs in the past.

Finally: in English, there is no space between a word and a comma (or period, semicolon) that follows the word. Typing like that may instinctively lead people to dislike you.

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