Sometimes people who are trying to help you online might ask for a full system report. There’s a variety of ways of doing this but one issue is that personally identifying details might be included, and this can be insecure — even your login name could give malicious interests vital information, but you should always keep your Mac’s serial number confidential.
EtreCheck is the answer, and will provide a report with the salient details included. it’ll also highlight problematic areas, with a More Info link so you can research. It’s free.