PARTICIPLES NOT CHECKED – Please help urgently?

I just don't understand the past participles. No matter how hard I try, everyone says something different: On YouTube, one person says "I laughed " (laughed: past participle), then another says "The switched-off cell phone" (switched-off: past participle). ChatGPT says "switched-off" = past participle, but the first participle is, for example, "lachend," isn't it? I…