This article assumes you've setup a bootable USB installer as in the using offline wallets tutorial. Now that you have the bootable USB drive, restart your computer and boot from it. Make sure you also have your second USB drive inserted that you will install Linux on.
For most computers either hit F2or Delete when the computer is first starting. This should load the BIOS menu. Choose the first USB drive as the boot device.
Choose Install Ubuntu Server.
Choose English again.
Choose your location.
Choose Yes to Detect keyboard layout. Follow instructions until keyboard layout detection is complete. Choose Continue.
For Hostname just enter ubuntu.
For Full name you can enter your name.
For Username enter your first name, all lowercase (or any name you want).
Set a password.
Choose Yes to Encrypt your home directory.
Choose Guided - use entire disk and set up LVM.
Choose disk to partition. You should have booted with your second USB drive inserted. If not you can insert it now and choose Go Back and then choose to Detect disk drives again.
Select your second USB drive.
This will delete all data on the drive selected. Be careful to not select another drive on your computer.
Write the changes to disks and configure LVM (choose Yes).
Set volume amount to max and choose Continue.
Write the changes to disks (choose Yes).
System will install.
Leave HTTP proxy empty.
Apt will be configured.
Choose No automatic updates. This won't have internet access anyways.
Don't choose any software to install. Hit tab and choose Continue.
Software will be installed.
For Install the GRUB boot loader to the master boot record choose Yes.
GRUB will be installed.
Installation will finish.
You are now done. It will ask you to restart. Choose Continue.
Now that Linux is installed you can continue with the using offline wallets tutorial.