How often does this happen to you: Your program crashes with a mysterious exception. You paste the crash logs into Google. The first link has a solution. Hooray!
You found this magical solution because some good samaritan in the past decided to share his or her notes.
You, too, can be a good samaritan! If you've ever come across a problem that had no solution easily found online, I invite you to share your work. You don't have to write a novel; it could even just be a sentence or two, as long as it's enough to help others out.
Here's a non-exhaustive list of ways to contribute:
As long as your work is public and indexed by search engines you're golden. Then someone can, in the future, be saved time and effort1.
In addition, if you find a solution to a problem online, thank the author! Leave a comment, upvote their answer, whatever. Appreciation feels good.
1 Fun story: I once Googled a problem and found a solution to it on StackOverflow... that I'd written three years previous. You might just end up helping yourself!