Firstly, I didn't realise that my system was not in fact UEFI, it was BIOS, so I had to use MBR rather than GPT partitioning, and I found out that I was BIOS from this:
[link href='https://askubuntu.com/questions/162564/how-can-i-tell-if-my-system-was-booted-as-efi-uefi-or-bios']Stack Overflow link[/link]
Then I didn't realise that [code]mount /dev/disk/by-label/nixos /mnt[/code]was literally meant to be input like that, I thought it had to be [code]mount /dev/sda1/nixos /mnt[/code]or something.
I then wanted to enable WiFi, which didn't seem to be working (I'd temporarily been using ethernet, but I need that for my main PC), so I installed lshw and got told that my wireless network card was disabled, and then
used [code]sudo ifconfig wlo1 up[/code]and found out it was due to 'rfkill'. Then I did [code]sudo rfkill list[/code]and found that my wireless LAN was being 'soft blocked'.
After which I ran:
[code]sudo rfkill unblock all
sudo ifconfig wlo1 up
And then I followed this (but used nmtu instead at the end):
And do [i]sudo nix-rebuild switch[/i] to make my new [b]/etc/nixos/configuration.nix[/b] active.
And then simply using the [b]nmtui[/b] command to settup my WiFi.
To add a user:
[link href='https://nixos.org/nixos/manual/index.html#sec-user-management']Nixos Manual[/link]
And to set the password: [b]passwd [(username)[/b].