In 1994 a researcher called Jakob Nielsen published ten usability heuristics, rules of thumb for judging any interface. Thirty years on they are still the industry's shared checklist, and once you learn even five of them you gain a slightly annoying superpower: you can name exactly why any app is irritating you.
Visibility of status: the system should show what is happening (the upload bar, the buzz after a payment). Match the real world: speak the user's language, "send money", not "create beneficiary". User control: undo exists, mistakes are cheap. Consistency: things do not move around or change meaning. Error prevention: make the destructive action hard to hit by accident. The other five are worth meeting when you are ready.
Heuristics power a technique called expert evaluation: before testing with users, a designer walks the product against the checklist and logs violations. It is fast and cheap, and it has a known blind spot, experts predict some problems and real users always find ones no expert predicted. Universities make you do both so you learn what each is for.
The dark side
Now invert everything. If you know exactly what makes interfaces effortless, you know exactly how to make the wrong choice effortless and the right one exhausting. These are dark patterns: the cancel button hidden behind four screens, the "free trial" engineered to be forgotten, the guilt-trip decline link, the countdown timer that is fake. Nothing about them is accidental. They are usability skill pointed against the user, and regulators in several countries are now legislating against them by name.
This is also where design stops being a technical subject and becomes an ethical one, which is a genuine part of the degree. You will be trained in persuasion. Whose goals you serve with it is a choice you make every working day.
Open three apps you use and hunt: find one thing deliberately easy that benefits the company (subscribing, allowing notifications, spending) and one thing deliberately hard that would benefit you (cancelling, deleting, saying no). Screenshot the best specimens. Once you start seeing dark patterns you cannot stop, and that is the point.
Nielsen's ten heuristics are free at nngroup.com and worth reading in the original. For the dark side, search "deceptive patterns", the site that coined the term keeps a hall of shame.