Custom log format documentation

Is there any documentation on how to make custom log format in

I don’t get all the S+ and s+ in the other formats.

I like to import logs with this format:
date time c-ip cs-username s-ip s-sitename c-version sc-status x-cache-info sc-header-size sc(Content-Length) sc-completed sc-bytes cs-bytes time-taken cs(User-Agent) cs(Referer) sc(CACHE_STATUS) sc(BALANCER_WORKER_IP) cs(X-Forwarded-For) x-origin-ip rs-bytes sc(ETag) cs(If-Range) cs(Range) sc(Content-Range) cs(Pragma) sc(Pragma)

Thank you