This is a quote from an essay on “Liberty” by John Stuart Mills.

“The peculiar evil of silencing the expression of opinion is that it is robbing the human race. If the opinion is rights, they are deprived of the opportunity for exchanging error for truth. If wrong, they lose what is almost as great a benefit; the clearer perception of truth produced by collision with error.”

Could anyone explain this quotes for me please....

It supports freedom of speech and expressions of opinion. If an opinion is wrong, after it's made public, others have the right and responsibility to correct it.