Not a problem, we're happy to help.
1. As an editor, when I proceed to the layout phase, all I have to do is to "browse" and "upload" a file after selecting the "layout" radio button?
Sorry -- I mis-wrote. To upload galleys that can be seen online, you have to make sure the "Galley" radio button is clicked.
2. This uploaded file must be a DOC or PDF file? Probably a DOC, because it should be handled by the layout editor, but I am not sure anymore...
This depends with how you are using OJS, and specifically whether you are using external layout editors. If you click the "Journal Help" option (should be in the journal sidebar) while viewing a submission's editing page, you'll get a fairly detailed description of the overall editing process, and how the layout editing step works. There are also a number of helpful tutorials here: http://pkp.sfu.ca/tutorials
, including some very specific ones on the layout editing process.
If you can tell me whether you are planning on using external layout editors, or are just planning on doing the galley editing yourself, and how you want to manage the layout process in general, I can provide a more complete answer.
4. Why do I get the message "DB Error: ERROR: invalid input syntax for integer: " after clicking in the "upload" button? It doesn´t happen always, but I can´t trace why and when it happens;
The following thread and patch may be of help: viewtopic.php?f=8&t=6053
. Make sure you only apply the pre-2.2.4 patch.
5. How do I know that the file has been correctly uploaded?
Try patching your system first, and then see if the upload process behaves normally. But typically, once uploaded you should be able to download it from that Layout section.