Using the following 6 steps install Magento2 on Ubuntu 18.04:

Step 1 – Install LAMP

Step 2 – Install Composer

Step 3 – Download Magento 2 Archive

Step 4 – Create Database and User

Step 5 – Create Apache VirtualHost

Step 6 – Run Web Installer

For complete detail visit: How to install Magento2 on Ubuntu 18.04?