I am quite confused as to Why God create life? Then only the theory of Karma and bhakti and merging with Him came in. But in the first place why did God Create Life? If you can clear some of my confusion I will be very much thankful to you.

Before we answer this question, first contemplate and try to find an answer to the following question: “Who created this confusion within you?”

What is the surest way to know the Creator's purpose for my role having been born as a human being?

You have now started thinking ‘What is the purpose of my Creation.’ That is the very purpose of Lord’s Creation.

What is the reason behind the Creator creating everything in pairs - truth and falsehood, man-woman, and so on when He Himself is One?

He has created everything in pairs for us to understand the difference between the Creator and Creation.

In the first place, why has the entire creation (all creatures, the Universe, etc.) evolved?

There is nothing called 'first place'. The origin and end are only in our mind.