The gist of it:

Occam’s razor states that when faced with several possible explanations for a phenomenon, the one that requires the fewest assumptions is most likely to be correct.

How to use it:

To apply Occam’s razor, ask: “What is the simplest and most likely explanation?”

E.g. You notice that a light in your home is flickering intermittently.

The simplest and most likely explanation might be that the light bulb is loose or faulty. Occam's Razor would suggest that you start by checking and tightening the light bulb or replacing it with a new one.

Instead of assuming more complex explanations, such as problems with the wiring in your house, a malfunctioning light switch, or electrical issues.

While these possibilities shouldn't be ruled out entirely, Occam's Razor encourages you to start with the simplest solution.

Deep Dive

In philosophy, a razor is a principle or rule of thumb that allows you to eliminate (or “shave off”) unlikely explanations for a phenomenon.

Occam’s razor, also known as the principle of parsimony, is a problem solving principle that states that among several possible explanations, the one that requires the fewest assumptions or entities is usually the most likely to be correct.

Why? Because the more assumptions there are, the more possibilities there are for error, and the simplest explanation is usually – but not always – the correct one.

This principle is often summarized as "Entities should not be multiplied without necessity" or "The simplest explanation is usually the right one."

Occam's Razor is a valuable tool in scientific and philosophical reasoning, as it encourages researchers and thinkers to prioritize elegant and straightforward explanations over complex and convoluted ones.

For example:

Imagine your smartphone's battery is draining much faster than usual.

Simple Explanation:
Applying Occam's Razor, you might first consider the simplest and most common explanation: a misbehaving app running in the background. You check your battery usage settings and discover that a particular app is consuming an unusually high amount of battery. You force-stop or uninstall the app, and the battery drain issue improves.

Complex Explanation:
Alternatively, you could jump to more complex explanations, such as a failing battery, a software glitch in the operating system, or even a hardware issue.

By addressing the most straightforward and likely cause of the problem, we avoid potentially costly solutions and are able to resolve issues efficiently and without unnecessary complexity.

Occam's Razor teaches us not to discount complexity when it is genuinely warranted. Rather, it calls on us to distinguish between complexity stemming from the intricacies of reality and complexity born out of cumbersome reasoning. By discerning the difference, we gain a sharper lens through which to interpret the world around us.

“Everything should be made as simple as possible, but not simpler.” – Albert Einstein

Sources:
9 Philosophical razors you need to know
Occam’s razor - A guiding principle of logic exhorting us to keep things as simple as possible
How to Use Occam’s Razor Without Getting Cut