You need some pre-requisites to install Hyperledger Composer.
Run the following commands in terminal to install pre-requisites for Hyperledger Composer:
$ sudo apt install npm
$ sudo npm install -g composer-cli
$ sudo npm install -g composer-rest-server
$ sudo npm install -g generator-hyperledger-composer
$ sudo npm install -g yo
Now to install Hyperledger Composer run:
$ sudo npm install -g composer-playground