If you create a new thread, reply to a post or edit your existing post (for latter you need to go to "advanced edit") just scroll down until you see "Attach files" and there "Manage attachments".
If my attached screenshots don't explain the process sufficiently just ask here again.
P.S. No need at all to apologise for language skills; and Google translator is fine. By the way: I usually use https://www.deepl.com/translator.