install laravel versi 5.3

misi numpang nanya, ini kok gak bisa ya bang pas installnya keluar bacaan gitu trus, knp ya?

 PS E:\training> composer create-project --prefer-dist laravel/laravel blog "5.3.*"
composer : The term 'composer' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the
spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:1
composer create-project --prefer-dist laravel/laravel blog "5.3.*"
~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (composer:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException