How do I understand the words "true" and "truth"? Good question. It has a lot to do with how my perceptual faculties link up with regions in my brain in which my concepts of these words is represented via networks of neural activity and connectivity. Incidentally, that's also how I understand the words "hello", "book", and phrases like "that ******* with the smart-aleck answer who thinks he's amusing."
More seriously, I don't subscribe to a particular theory of truth, even a personal one. I tend towards correspondence theories of truth, and I am absolutely against relativism (or at least the strong versions; I believe there exists objective truth even if we are sundered from it), but am hampered by issues like what a proposition is. Time also presents an issue for me as I do not agree with Aristotle here. I believe statements about the future do have truth values, but these do not entail fatalism. Thus a statement about what the average global temperature will be in 2080, for example, is necessarily true or false. Let's say it is true. Aristotle argued that this is tantamount to saying that therefore the average global temperature in 2080 is necessarily going to correspond to the statement about it made in the present, and therefore the future is fated to be in accordance with the truth value of the statement. He didn't like this fatalism, but his way out is not my own. I don't see the necessary truth (or falsity) of a statement made about a future state of affairs to entail a necessary state of affairs corresponding to the truth value of the statement, but rather that the realization of the future state of affairs licenses the necessity of the truth value of the statement made in the past.
Relativity, however, presents a further challenge. If reality is really 4-dimensional, and from different reference frames what will happen from our perspective has already happened (and we are 4-D "hunks of matter"), then any statement about the future has a truthmaker already in some form via some set of reference frames in which the state of affairs the statement concerns has already been realized.