First and foremost I must say this is a simple explanation, it’s not extensive.
There are two core facts in understanding the defense for our hope.
We know a Creator/Supreme Supernatural Being exist for the fact that there is overwhelming evidence due to the detailed explorations of science through Astronomy, Cosmology, and Biology; in addition to the fact that there is no way to concretely prove He does not exist.
The Holy Bible is the written source for the Christian Faith (not Jehovah Witnesses or Mormons). Therefore, true Christians believe that the Creator/God that exists is the Covenant God of the Holy Bible.
After these two facts (and also according to Paul in Romans 1:20-21) its obvious one cannot rationally (legitimately, validly) deny the existence of God. And as we are about to see, the Bible cannot be rationally denied as well. So note it, understand it, and memorize these two facts, because in order to properly explain and/or defend our Faith as irrefutable truth we have to make sure these two facts remain coherent (agreeable).
Now that the core facts have been stated, let’s move onto a more literal documented fact. The Bible—which was written over a span of 1,500 years by roughly 40 different authors—has been sourced by the scientific, academic, and philosophical (non-religious) communities as a historical document due to the accuracy of the people, places, events, and track record of fulfilled prophecies within in it. No other religious manuscript has been vetted and shown to be accurate more than the Holy Bible. Thus, all other religions are banking their so-called "truth" (and lives) on unvetted and unproven manuscripts. Therefore, continue to hold fast to these facts as solid evidence for the trustworthiness of the Bible.
The core and documented facts we just discussed now lead us to three “Faith facts”—facts of our Faith. As Christians, these Faith facts we ourselves need to know (believe and accept) to be the undeniable truth.
Faith fact #1: God is in control of all things past, present, and future.
Faith fact #2: The Holy Bible is God’s divine Word to us, everything that is written in it is exactly what He wants us to have, no more no less.
Faith fact #3: Because God is in control of all things and the Bible is His Word to us, He would never allow anyone nor anything to tamper, change, add, or take away from what was is in our written source to Him. As a result, He has protected and preserved its originality and trueness from the moment it was written, up to now, and forevermore.
Considering the two core facts, the historical actuality (people, places, events, and the track record of fulfilled prophecies) of the Bible cited by Christians and reputable non-Christians alike, and the three “Faith facts”, one can see the logical reasoning in understanding why the Christian tenaciously (uncompromisingly) believes and claims that the Bible and its information inside are flawless. Indicating the life, purpose, and divinity of Jesus Christ is truth and reality. These facts, along with the testimony of the original witnesses of Jesus, one can’t substantially (with concrete evidence) deny the Christian's claim of the Bible's authenticity. As long as this is the case, the Bible will be authentic until proven otherwise (not that there will ever be an otherwise).
Standing on the two core facts, the historical documentation, the three Faith facts, the testimony of the original witnesses, and the testimony of what you’ve experienced to be true and what Jesus has done for you—as well as any other facts you may possess—is an adequate defense for our hope.
Note: Possessing some knowledge of Church history, other religions, as well as science and philosophy is a tremendous asset to have for proving and defending the case for our Faith. Moreover it will also strengthen one's own personal foundation and faith.