This meta topic is meant as a reference to users asking questions along the lines of "I was following this tutorial/guide/whatnot [link] and got an error message, how do I fix that?". I'll provide my own point of view in an answer, alternative points of view are welcome.
In essence, you must reproduce the key steps you took from the tutorial in your question, and be careful about which tutorial you pick.
questions and answers on this site are meant to be self-contained. If you ask a question referencing a tutorial explaining how to set up
awesome_server, people having problems with it will search for "awesome server" and find your question. If the link to the tutorial in your question is no longer valid, they will get no value whatsoever from the question and any answers it will receive. Your post will in fact have negative value for them, since it will hide more complete questions and answers they could have found otherwise.
more often than not, the issue is not with the tutorial itself, but with the way you understood and followed it. This is one more reason to include the key steps that you took from the tutorial in your question. For instance, if the tutorial was using EXT4-formatted drive and you took an NTFS-formatted drive instead, there's no way to discover it unless you post the commands you have used to format or mount the drive.
on a related note, if you could not get through the whole tutorial (getting expected results in every step), there's no way for others to know where you got stuck unless you tell this. One more reason to post the actions you performed and the results you've got, even if you copy-pasted every command verbatim from the tutorial page.
finally, be wary of blindly following a series of steps you don't fully understand. For example, I once myself followed a tutorial which resulted in nothing more than a big security hole. Essentially, unless the tutorial you're using is the official one, there's no guarantee that it will work for everyone, it's just something that may have worked for the person who wrote it.