Three words get mixed up constantly. Keeping them apart is half of logic.

• True / false apply to statements. "Water boils at 100°C at sea level" is true.
• Valid / invalid apply to arguments. An argument is valid when it is impossible for all the premises to be true and the conclusion false. Validity is about structure: the conclusion follows.
• Sound means valid and all premises actually true. A sound argument guarantees a true conclusion.

Valid but false

All cats can fly. Tom is a cat. Therefore, Tom can fly.

This is valid: if the premises were true, the conclusion would have to be true. It is not sound, because the first premise is false.

True but invalid

Some people are doctors. Paris is in France. Therefore, the Earth orbits the Sun.

Every statement here is true, but the conclusion does not follow from the premises at all. Invalid. True premises and a true conclusion do not make an argument good.

The two ways to attack an argument

1. Show it is invalid: the conclusion doesn't follow, even if the premises are granted.
2. Show a premise is false: it follows, but it starts from something untrue.

Connection to Universal Humanism: UH's correspondence theory of truth handles the premises (do they match reality?), and logic handles the structure (does the conclusion follow?). A good argument needs both.