How students can retain what they learn and actually turn it into usable skill.
Completing a course and then forgetting almost all of it is an extremely common experience, and it happens because consuming information and building usable knowledge are entirely different processes. Watching or reading feels like learning, but without active engagement and application, most of it fades within weeks.
The first fix is to learn actively rather than passively. Take notes in your own words instead of copying, pause to test yourself on what was just covered, and after each section try to explain the main ideas from memory, because retrieving information is far more powerful for retention than reviewing it. Explaining a concept aloud as if teaching someone is one of the most effective techniques available, since it immediately exposes what you only think you understand.
The second and more important fix is to apply what you learn quickly and repeatedly. Knowledge that is used becomes skill, while knowledge that is only stored decays, so build something with it, use it in a real task, or solve actual problems with it as soon as possible, ideally while still learning rather than after finishing. This is why project based learning works so well, and why learning something you have an immediate use for sticks so much better than learning in the abstract.
Finally, revisit deliberately. Review key material a few days and then a few weeks later, because spaced review is what moves knowledge into long term memory. Keep organised notes you can actually return to, and consider maintaining a personal record of what you learned and how you applied it. Also be realistic and avoid rushing through many courses, since finishing one course and genuinely applying it is worth far more than completing five you never use.
Example: Someone who finishes a course module and immediately builds a small project using it will retain and be able to use that knowledge, while someone who finishes the whole course first usually forgets the early sections.
One practical tip: Apply what you learn immediately, ideally while still doing the course. Knowledge used becomes skill, while knowledge merely stored fades within weeks.