First you need to login to cPanel and select the Softaculous Script Autoinstaller.
Once you have done that, select the E-Commerce category and then click on OpenCart from the dropdown menu.
Once you have selected OpenCart, click on the Install button on the upper right corner of the page.
This will display the needed configuration page before your script is installed.
In the first section you need to select on which domain the OpenCart will be installed and how to be accessed.
Unless you have an SSL certificate already purchased and configured, please leave the "http://" in the "Choose Protocol" dropdown.
Then select the domain name you want your store to be installed on.
Leave the "In Directory" box empty if you want your shop to be directly accessible by your domain.
If you type "ocart" for an example, your store url will become http://yourdomain.com/ocart/
You can also choose the name of the database which your OpenCart store will use to store its data in.
The Softaculous auto installer usually generates a random name and if you do not understand or need to change it, you can leave it this way.
The second section is about your store's owner and contact information.
Here, you can type your contact details and store name. You can always change your contact information by configuring OpenCart from the OpenCart admin panel.
The last section is for configuring your OpenCart admin user and password.
Once you enter the details for your admin user, hit the "Install" button and OpenCart will be installed on your account.