The usage of chown and chgrp

sudo chown -R username:group directory
will change ownership (both user and group) of all files and directories inside of directory and directory itself.

sudo chown username:group directory
will only change the permission of the folder directory but will leave the files and folders inside the directory alone.

chown user: file (Note the left-out group), it will use the default group for that user.

Cited from http://askubuntu.com/questions/6723/change-folder-permissions-and-ownership

You can change the group ownership of a file or directory with the command:

chgrp group_name file/directory_name You must be a member of the group to which you are changing ownership to.

Cited from http://unixhelp.ed.ac.uk/tasks/change_own.html