Context: a well-known murderer tells an anonymous bulletin board that he's gonna kill everyone in that thread.
nanashi-san atto oopun 名無しさん＠おーぷん Anon @ open.
Open probably refers to open 2 channel, おーぷん2ちゃんねる, a bulletin board based on 2ch.
The incrementing numbers 193, 194, 195, 197, 197, and so on at the left side of each response is the identifier used to cite what a previous user posted.
The 2017/11/×× is the date. Japan uses a year-month-day date format. The ×× where the day would go is a placeholder used in fiction in places where a specific name or number isn't necessary. See ○, ×, and △ for details.
tsuchi 土, "dirt," inside parentheses next to the date refers to the weekday: doyoubi土曜日, "saturday."
