Question:Can you clarify to me the first fruit I must give unto God in reference to my income? I get paid monthly. What will be my first fruit offering unto God?
Firstfruits is a concept taught in the Old Testament. While the concept is carried over to the New Testament, it is not directly applied to income. See "What is meant by "first fruits"?" for details.
But generally, what people refer to as firstfruits in regards to giving to the Lord holds a similar meaning to what is found in the Old Testament. The question is how do we prioritize our spending. Do we spend what we want first and then decide how much of the leftovers to give to God or do we decide in advance what is God's and then fit the rest of our spending in the remaining part? See the article "Planning for Uncertainties" for information about setting priorities with our funds.
If you are asking about amounts, the New Testament does not set a fixed amount to give. Instead, it is to be an individual's choice based on the amount he is prospering (I Corinthians 16:1-2). "For if there is first a willing mind, it is accepted according to what one has, and not according to what he does not have" (II Corinthians 8:11). I cannot tell you how much to give. Some find that too vague and demand more specific guidelines. To these I point out that the Israelites were expected to give ten percent of their profits. That should give you rough guidance for your own decision.