Step1: First you need to check composer install on system or not.
Type below command on your console to check composer installation
If not install than install it . using below command.
curl -sS https://getcomposer.org/installer | php mv composer.phar /usr/local/bin/composer
The first command install Composer into your local directory,
the second will move the composer.phar file to a directory
where it can be accessed globally by your system.
Again check below command
Step 2: Install magento project on local machine, Type command on console.
composer create-project magento/project-community-edition magentodemo root@system:/var/www/html# composer composer create-project magento/project-community-edition magentodemo
you see below output on your console
Installing magento/project-community-edition (2.0.2) - Installing magento/project-community-edition (2.0.2) Downloading: 100% Created project in Magento Loading composer repositories with package information Authentication required (repo.magento.com): Username: bfba1bb4bdfdcb63d8458457728f Password: Do you want to store credentials for repo.magento.com in /home/gaurav/.composer/auth.json ? [Yn] Y
Step3: After this you need username and password
https://www.magentocommerce.com/ and login into your account and than go to Develoers >> Secure Keys and generate key here. Basically public key is belong to Username Private key is belong to Password
Step4: Give the permission of the folder
sudo chmod -R 777 magentodemo/
Step5: After that put below url on your local browser.
If you want to add sample data on your project than run
below command on console after complete install project.
php <your Magento install dir>/bin/magento sampledata:deploy