Thanks for your question.
Because the documents we have were all hand copied (printing was not invented until the 15th century AD) there are variations in the text. Most are simple copying errors, some appear to be marginal notes incorporated into the text, some seem deliberate to emphasise a particular point. Other variations have no discernable logical explanation.
The documents available today number several thousand.
Fortunately none of the variations affect doctrine, but do require a choice to be made on the most likely ‘original’ wording.
The New Testament is affected more than the Old because the Jews were more scrupulous in their copying methods.
So you will encounter terms like ‘Textus Receptus’ (Recieved text); Majority Text; Nestle-Aland; and Westcott and Hort text, etc.
For a student’s guide to textual variants see: http://www.ovc.edu/tc/index.htm
Each generation of scholars has the idea that an improvement in translation can be made. Some are made to improve what is seen as the outdated language of the King James Version.
Some believe that manuscripts that have been found since AD 1611 have variations which can be viewed as more authentic than those used by the KJV translators.
Not all scholars are agreed on a particular set of text, neither will they ever be this side of the Kingdom of God. Translators who believe that the words of the original Hebrew and Greek scriptures are inspired by God (as the scriptures themselves claim) make their translation as near as possible on a word for word basis. Such were the King James translators.
Word for word translations are not always easy to understand because we have to know and take into account idioms of the Hebrew and Greek language. They do however, by use of Concordances and Hebrew and Greek lexicons, allow us to see for ourselves how the words are used elsewhere. The value of this cannot be overstated. With the advent of computers this is more easily done than ever before.
Translators who do not believe that the words of the original Hebrew and Greek scriptures were inspired by God, but rather an ‘evolution of ideas’ by gifted men, make their translation on a ‘meaning for meaning’ basis.
They also have a different set of criteria for choosing textual variants.
This, as you can surmise, puts you into the grey area of the translator’s predilections and you cannot compare scripture with scripture because you have no way of finding similar passages. The translations will be easy to read and understand in themselves but will be biased with the translators beliefs.
To take one extreme example – Jehovah’s Witnesses fell into the trap of not liking what they read in the King James translation, so made their own translation which says what they want it to say.
Everyone who wants to understand the Bible faces the problem raised by your question. English translations are not inspired, whereas the Hebrew and Greek originals were.
John 10:35 ...scripture cannot be broken;
2Timothy 3:16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
It seems to me logical therefore to use as your main Bible a translation which allows you access to the original language and other translations to compare the range of possible meanings for any passage you find difficult.
I will, however, repeat that the greatest help to understanding the Bible is to compare how the original words are used in context elsewhere in the scripture. The Word of God has thousands of themes running through it connected by God’s use of both words and phrases. All placed there for our edification.
If a particular translation doesn’t allow us to find them, it is of limited value.
I hope this helps.