Go the site and download the .iso image file to get the latest version.
You can mix and match HDDs but keep in mind that you will need connection adapters to go from PATA to SATA or IDE to SATA.
And also, it's a good idea to change your CMOS battery if the computer is old enough.
Select the .iso file and the USB drive you want to use and click start.
Once the USB drive is created you can plug it into your server and boot from it.
Remeber to change the boot order in the BIOS to boot from the USB drive first.
Follow the on-screen instructions to install OpenMediaVault on your server.
Open a web browser on your computer and type in the IP address of your server.
The default username is "admin" and the default password is "openmediavault".
Once you are logged in you can start configuring your server. 
Once the drives are wiped you can go to Storage > File Systems and create a new file system.
Select the drives you want to use and click create.
Once the file system is created you can mount it and it will be available for use.
You might need to reboot your computer throughout this process.
Once you are connected you can start using your home server to share files and access your data from anywhere.