What is Critical Thinking?
Critical thinking is a systematic process for separating truth from fiction. It provides tools of thought for carving your way through the flood of information that you face each and every day. It does bear many resemblances to the scientific method, but it is more applicable to the vague and incomplete information one faces in daily life. Whereas science deals primarily with the physical realm and impartial experimentation, critical thinking deals with your own thoughts and experiences, plus secondhand knowledge gained from outside sources. The rigorous approach of science is untenable in this context due to the fuzzy decision-making, incomplete data, and an excess of variables which cannot be isolated. Critical thinking is a better tool for day-to-day human existence.
Here is a metaphor to understand the general process of critical thinking. Imagine a space colony which encloses itself in a glass dome, like one you might find in science fiction. This colony has to protect itself from the harsh world outside. In particular, there are many highly infectious diseases roaming about in the air outside the dome. There are also external factions who are enemies of our little settlement, and might try to send spies or saboteurs to infiltrate it.
When a person shows up at the gate outside the dome, they are not simply allowed to stroll in the front door. There is a stringint screening process. Perhaps initially they must identify themselves through a speaker system, explain their business at the colony, and show identification. Even once admitted, they are not immediately allowed onto Main Street. Instead they go into a quarantine area, perhaps an airlock, where they can be scanned for microbes or weapons. Depending on the visitor's claimed identity, colony members are called in to identify the visitor and corroborate their story. And even once out of the quarantine and into the colony itself, the visitor may be escorted by a security guard or given a identification badge. The may be forbidden from entering sensitive areas of the colony, such as the main control room.
In critical thinking, your mind is like this this colony. There are a million pieces of information that assault your senses every day, but only some of them have any merit at all; and only a very select few should be integrated into the core of your mental framework, to become a permanent part of your worldview, and a basis for your future behavior.
Information which does not pass this screening process is not necessarily just forgotten, but it will be carefully quarantined or otherwise flagged as dubious or uncertain. This way, you do not risk considering it as truth by mere virtue of its relative age in your mind.