This is the best explanation I’ve seen of the RT-PCR test, and why, the way it is being used, it throws off so many false positives. From Dr. Pascal Sacré at globalresearch.ca:
Introduction: using a technique to lock down society
All current propaganda on the COVID-19 pandemic is based on an assumption that is considered obvious, true and no longer questioned:
Positive RT-PCR test means being sick with COVID. This assumption is misleading.
Very few people, including doctors, understand how a PCR test works.
RT-PCR means Real Time-Polymerase Chain Reaction.
In French, it means: Réaction de Polymérisation en Chaîne en Temps Réel.
In medicine, we use this tool mainly to diagnose a viral infection.
Starting from a clinical situation with the presence or absence of particular symptoms in a patient, we consider different diagnoses based on tests.
In the case of certain infections, particularly viral infections, we use the RT-PCR technique to confirm a diagnostic hypothesis suggested by a clinical picture.
We do not routinely perform RT-PCR on any patient who is overheated, coughing or has an inflammatory syndrome!
It is a laboratory, molecular biology technique of gene amplification because it looks for gene traces (DNA or RNA) by amplifying them.
In addition to medicine, other fields of application are genetics, research, industry and forensics.
The technique is carried out in a specialized laboratory, it cannot be done in any laboratory, even a hospital. This entails a certain cost, and a delay sometimes of several days between the sample and the result.
Today, since the emergence of the new disease called COVID-19 (COrona VIrus Disease-2019), the RT-PCR diagnostic technique is used to define positive cases, confirmed as SARS-CoV-2 (coronavirus responsible for the new acute respiratory distress syndrome called COVID-19).
These positive cases are assimilated to COVID-19 cases, some of whom are hospitalized or even admitted to intensive care units.
Official postulate of our managers: positive RT-PCR cases = COVID-19 patients. 
This is the starting postulate, the premise of all official propaganda, which justifies all restrictive government measures: isolation, confinement, quarantine, mandatory masks, color codes by country and travel bans, tracking, social distances in companies, stores and even, even more importantly, in schools .
This misuse of RT-PCR technique is used as a relentless and intentional strategy by some governments, supported by scientific safety councils and by the dominant media, to justify excessive measures such as the violation of a large number of constitutional rights, the destruction of the economy with the bankruptcy of entire active sectors of society, the degradation of living conditions for a large number of ordinary citizens, under the pretext of a pandemic based on a number of positive RT-PCR tests, and not on a real number of patients.