I wanted to know how does the contribution section in our profile works?

You can read about it here

I also don't know how it is showing +3 in my profile. Is it due to the comments I made in the recent contest blogs?

Yes, due to comment which got upvoted by others (shown with green triangle on top-right corner of your comment). Getting downvoted can reduce your contribution (may even go negative)

Tips for not getting downvoted by $$${\color{red}{\textbf{antontrygubO_o}}}$$$

This one by $$${\color{red}{\textbf{Errichto}}}$$$ might be relevant for you.

It's bad if your question was already asked or you ask for help without doing some work yourself