crosh>shell developer mode on chromebook

I have a Samsung Chromebook OS and i’m in developer mode. I want to get android apps and linux on my laptop, i know how to get into the terminal it pulls up in a tab and i can enter shell but when installing crouton i run into a problem with the Error: sudo command unknown, it says unknown command every time i enter in a command. how do I make it read My commands am i not opening the Terminal right?