Troubleshooting

Hey everyone hope yall are having a great day I have been trying to learn fire alarm trouble shooting for a while now I know the process but I still dont understand the readings on the meter I know the lower the number the closer you are in ohms I know to check for continuity and all that but when it gets to 500k ohms or 50k or stuff in the k or m and I dont know what to do or what is bad and I just need someone to explain it to me shorts opens are the easiest but mainly shorts and earth grounds are so confusing people meter them with DC and all that I don't understand it can someone explain it?