What happens if the assertion is true? And what is the basic idea behind these assertions?

Answer 1

it means it only return False or True..if false raise assertion error and stops next instructions in its vicinity..if true No error ,and continue the execution.... assertion is useful for testing the functions...or conditions that we write.

Answer 2

When it true it can insert to the if part, and do what you want. the program not stop as error aqured.
You useuly use assertions for testing.