install angular cli

1npm install -g @angular/cli
2ng new my-dream-app
3cd my-dream-app
4ng serve

1npm install -g @angular/cli@6.1.1

1      
2        content_copy
3      
4      npm install -g @angular/cli
5    

1npm install -g @angular/cli    //make sure you have node/npm installed 
2ng new <appname>        //  eg:  ng new my-app
3cd <appname>       // cd my-app
4ng serve

1Install Specific Version (Example: 6.1.1)
2npm install -g @angular/cli@6.1.1

1npm install -g @angular/cli
2ng new my-app
3cd my-app
4ng serve