Default [Q] Help getting slimkat flashed to my Nexus 5

I am trying to install slimkat onto my nexus 5 but for some reason I cant get ADB to flash it onto my phone. I have the ROM .zip downloaded on my computer along with the gapps add on. When I give ADB the prompt to flash-all I get a message saying that the syntax of the command is incorrect. I've tried extracting the files but it gives me the same message.