Words of the living LDS prophets

Hello,

My name is Tony. I'm new to this forum. I come from a evangelical
Christian background and live near Toronto Canada.

I started viewing some material from the church.

I was reading Gospel Principles. On page 55, it says "In addition
to these four books of scripture, the inspired words of our
living prophets become scripture to us. Their words come to us
through conferences, Church publications, and instructions to local
priesthood leaders."

How do Latter-day Saints unanimously decide if the words of
past and present LDS Prophets are inspired (to be accepted
as scripture), are speculative, or are in error when they speak
at General Conferences?

Suppose for example that 50% pray to God and obtain one answer and
the other 50% get the opposite answer - who decides what is true,
what
is false, and what is just speculation?

Thank you.

Tony