Moving to Linux

[ppppenguin]

Having successfully installed Mint on a couple of PCs (a couple of old laptops that I was giving away) I'm struggling to get it installed on the PC I want to use as my Linux testbed.

1: Mint Cinnamon on USB stick
2: Set BIOS so it will boot from USB
3: Live Linux boots with no trouble
4: Install Linux Mint
5: Choose language and localisation
6: Install 3rd party software
7: I then get a screen with the attached photo (1)

I don't understand this and searching online hasn't helped. The HDD (actually a Crucial 512GB SSD) has a windows system on it at present which I want to erase, as if starting with a brand new HDD. 

The PC is an HP minitower from about 2011 with a Sandybridge series G630 CPU and 16GB RAM. I've been through the BIOS settings, disabling UEFI, not that it made any difference. Boot order is USB, then HDD. BIOS can see my SSD. Live linux can see my SSD and its contents.

My main reference is: https://linuxmint-installation-guide.rea...index.html

In previous instals I got the 2nd attached photo.  I understand this and chose "Erase disk and install Linux Mint". I didn't use it on previous instals but I suspect that LVM is a good thing as it allows easy re-partitioning.