Difference Between Helpful Reply vs. Correct Reply
If someone replies to your question with useful information, it's good practice to mark their reply as either Helpful or Correct.
Doing so will allow others who have the same question can quickly see which replies are the most useful. A Helpful reply is on the right track, while a Correct reply answered your question. Correct and Helpful answers also allow the creator to earn reputation status points.
Once a reply is marked as Correct, it is then displayed in the just after the original question making it easier to find without having to read through the entire discussion thread.