Help installation

[Franck Olivier Ngassam Nyakam]

Hello sir
 I want to install Xcrysden on my mac but for this I have to install macport. I 
have followed all the installation procedure may when I have to enter the 
command.port install xcrysden +x11.. I have this messageError: Insufficient 
privileges to write to MacPorts install prefix.how to do please? thank you