A valid argument is one where the premises are true and the conclusion
can not be false. In other words, the premises are true and the
conclusion must be true.

All cars have four doors
Henry has a car
————————
Henry’s car has four doors

This is a valid argument. If the premises are true, the conclusion must be true. Notice that the premises are not actually true. Namely that all cars have four doors, yet the argument is still valid. If all cars have four doors and Henry has a car, then Henry’s car has four doors is valid.