Can someone give me a real life meaning of invalid argument form?

Answer 1

If dogs do not exist, there is no Lassie or Rin Tin Tin.

Dogs exist.

Therefore, there is Lassie or Rin Tin Tin.

"Invalid" simply says:  even if a person agrees with the major and minor premises, that person may disagree with the conclusion.

The premises do not "guarantee" the conclusion, i.e., the argument or case is not "air-tight."

"A Philosophy of Universality," O. M. Aivanhov.

Answer 2

God exists.