When you kill a person that's murder.
The readings are the kun'yomi vocab readings. So, if you know 人's reading as a vocab word and 殺す's reading, you should be able to read this word. Just note that ころし goes to ごろし due to rendaku.
If you commit murder, you must go to prison.
I heard there was a murder in this neighborhood yesterday.
I thought it wouldn't be fun to lead a calculating life, so I'd just do whatever I please, but I ended up becoming a murderer before I knew it.