About the "Find a bug" section
When you have solved a problem and received an "Accepted" for it, you have the opportunity to look for bugs in the submits of other students on this problem. Namely, a link "Find an bug" appears on the problem page, which opens a list of specially selected incorrect solutions to this problem. (Of course, the link does not appear in every problem, but only in those problems where there are such specially selected solutions.) There is also a section in the site menu "Find a bug", where there are links to all solutions in which you can look for errors (not all of these solutions are available to you — solutions are available to you only for those problems for which you received a "Accepted").
For each of the solutions in which you need to find an error, it is known that the error can be corrected by making no more than 15 edits in the solution code. An edit is considered to be adding, deleting, or changing one character (i.e., the Levenshnein distance is actually considered). Your need to find the error, fix it, and get OK on the problem. To give you some margin, you are allowed to make up to 23 edits.
In the "Find a bug" interface, you are immediately given a text editor in which the solution code is open. I strongly recommend looking for errors directly in this editor, without copying the code anywhere (like your IDE or editor), and accordingly not using a debugger, etc., but only looking at the code with your eyes. But in the most difficult cases, you can copy the code and understand it more thoroughly.
The solutions in the "Find a bug" section are available in different programming languages. Don't be afraid to look for bugs even in languages you don't know. I try not to allow those solutions in which the error is caused by language problems to search for errors, almost always errors have more algorithmic reasons, and, accordingly, you can find them, even if you do not know the features of the language.
I do not look at the solutions sent through the "find a bug" section with my eyes and do not comment (in particular, it is impossible to get "accepted" for them), and they do not affect your results in the rankings. Of course, if you can't find an error, you can write to me, I will advise you something.
Each solution, in addition to the problem, is also characterized by an individual number (a combination of four letters or numbers). Use this number to distinguish between solutions for finding errors for the same problem; in particular, if you want to ask me about such a solution, then specify both the name of the problem and the number of the solution (well, or just send a link to the error search page in this particular solution).