I need help reading Syntax in Ubuntu!?

That's a standard unix command usage format message which a command will give you when invoked with inappropriate arguments or with the -h or -? flag. Basically, something tried to invoke the command "unshield" with arguments the command did not understand so it spit out the command argument format under the assumption that whomever invoked the command needed a little help in doing so. Anything inside square brackets ( "[" and "]" ) are optional, anything separated by the pipe symbol ("|" ) is an alternate flag or argument, that is the argument "c|g|l|t|x" indicates that it's expecting the argument "c" or the argument "g" or the argument "l" or the argument "t" or the argument "x". You should be able to call up a more detail description of the command by just typing in "man unshield". If for some reason, the man page for unshield was not installed on your machine just google for "man unshield". Chances are that "cabextract" was just a script and it invoked "unshield" to do it's bidding but for some reason invoked it with the wrong arguments. You might want to do a "file `which cabextract`" to see if it's a script and if it is do a "less `which cabextract` to read it to see if there's any information in the comments within the script, the backquotes are important as it means use the results of the command within the back quotes for example the command "file `which ls`" is the same as "file /bin/ls" because "which ls" returns "/bin/ls". Note that cab files are actually intended for Windows based operating system and though there are utilities in Linux to manipulate them, cabfiles are not used to package programs for Linux.