Is there a way to upload a file regarded to my question, because a member ask me to check the file? What is the right way to do this? I checked about this in meta questions but I didn't find one? Thanks
You can upload images quite easily, via the button (or Ctrl+G).
You can easily include the contents of a file, using either the blockquote or preformatted buttons (Ctrl+Q and Ctrl+K) respectively.
Typically, this is all you would need - if it comes down to inspecting a specific file, this would typically show that the question should be closed as "Too Localized". If you have e.g. some specific log records, or some specific lines of code, include it as content.
I find it hard to imagine what scenario you would legitimately need to actually include an actual file.
(But if you do, then see @Lucas' recommendation to link to external file sharing services such as Dropbox, etc.)