Please help me to understand what is meant here. If Jesus was "a god" then He could be THE God or a false god. What else could this mean? How can Jesus be "a god"?
Aunty Jane explained what you need to know about the difference between The Theos and Theos. That difference is shown in these 2 translations.
James Moffatt New Testament
"THE Logos existed in the very beginning, the Logos was with God, the Logos was divine."
Goodspeed New Testament
"In the beginning the Word existed. The Word was with God, and the Word was divine."
Moffatt and Goodspeed both show they see Theos in John 1:1c as descriptive as it lacks the definite article. That is what is understood by using “a god.”
Consider these commentaries.
Robert Young - Concise Commentary Commentary on the Holy Bible
“AND THE WORD WAS GOD,] more lit. ‘and a god (i.e. a Divine Being) was the Word’ that is, he was existing and recognized as such.”
"According, from the point of view of grammar alone,[theos en ho logos]could be rendered "the Word was a god." This leads me to affirm that one may not infer from [Colwell's]rule 2b that anarthrous predicate nouns which precede the verb are usually definite. Indeed, such nouns will usually be qualitative in emphasis."
Murray Harris - Jesus as God - The New Testament Use of Theos In Reference to Jesus (pg 312)
"There is a distinction in the Greek here between 'with God and ‘God'. In the first instance the article is used and this makes the reference specific. In the second instance there is no article and it is difficult to believe that it's omission is not significant. In effect it gives an adjectival quality to the second use of Theos so that
the phrase means 'The Word was divine.'"
The Translators New Testament.
It is true that the great majority of translations say the Word was God. The trinity has dominated Christianity for 1,600 years. It is deeply ingrained. But the real question is, what does the Bible really teach? Other “proof” texts for the trinity are either vague or disputed just like John 1:1. That Jesus is the Son of God is crystal clear.