Truth is eternal and lie always forgettable.
The truth is something that actually happened or something that is real. A lie is usually something that is made up or a fantasy about what happened.
A lie is much easier to identify than the truth. A lie is a statement made with intent to deceive. The intent is the key here: If I tell you that New York is in Canada, and I really believe that, then I'm not lying, even though the statement is demonstrably untrue, because I myself believe it - I am TRYING to tell the truth. On the other hand, if you are not sure where New York is, and I tell you it's in Canada - maybe because I want to you fail a test, look silly or whatever - then I have told a lie.
We often speak of "white lies", ie lies told with good intentions. For instance, if a friend's outfit doesn't look good, but s/he has no time to change it, it's kinder to say "you look great" than to be honest. Technically this is still a lie, it's just that most of you wouldn't consider it wrong.
But as for what truth is - we may agree on physical facts, but abstract "truth" is a very tricky concept. We can only say that, if you are trying to be honest, then you are, as far as you know, speaking the truth.
We often speak of "white lies", ie lies told with good intentions. For instance, if a friend's outfit doesn't look good, but s/he has no time to change it, it's kinder to say "you look great" than to be honest. Technically this is still a lie, it's just that most of you wouldn't consider it wrong.
But as for what truth is - we may agree on physical facts, but abstract "truth" is a very tricky concept. We can only say that, if you are trying to be honest, then you are, as far as you know, speaking the truth.