Formally, as pertains to logic, it doesn't really matter. All that matter is the a proposition can hold two values; true and false, and that truth is not identical to falsehood. Indeed, many logicians (especially those of a mathematical bent) dispense with 'truth' altogether and use binary; 'true' is equivalent to '1' and 'false' is equivalent to '1'. The point of this is that as long as all true things have the same value ('true') and all false things have the same value ('false') we can do logic without committing to a substantive semantic definition of 'truth'. On this approach a valid logical system is one in which from premises with a value of '1' conclusions with a value of '1' can be derived. The point is to assess the validity of the system, rather than whatever value the system contains.
Of course, the validity of the system would not concern us very much if we did not think that the value within the system was important; we do logic partly because we think that value is important. And it is unlikely that we think binary values particularly important (why would '1' be better than '0'?). Consequently the binary approach does, if we want it to be epistemically interesting, presuppose either that we already have adequate understanding of truth or that it can be acquired.
But is this really such an extravagant presupposition? You ask 'What is truth' but I do not for a second believe you do not understand the word 'truth'. Surely, when someone says 'Speak the truth, the whole truth and nothing but the truth' you do not make the characteristic sound of confusion that a person makes when confronted with a sentence they find incomprehensible (consider: 'Speak the purple, the whole purple, and nothing but the purple'). Quite plausibly, this understanding is enough for our purposes (if not, why not? Do you have purposes different to those of logicians?).
If you want your question answered in a substantive way, I am afraid you will have to read some primary literature. It is not a subject I can do justice to within a brief paragraph (especially given I have not come to my own conclusions as to the correct account of truth). Perfunctorily, I would probably take it that a proposition is true if and only if it is the case. Truth is that property of propositions which occurs when they are the case. I am sure the next question you will want to ask is what does it mean for a proposition to 'be the case'. This is not a trivial question. But if we find it difficult to answer in the form of definition that does not mean that the previous definition is deficient or the project in which we are engaging futile. Again, understanding can, must and does intercede at a brute level, at some point (and where it is needed, depends on our purposes).
comes from a and lethe, the latter meaning forgetfulness. So truth in Greek literaly means that which is intact memory-wise.
