I’m not that experienced myself so I’ll only describe the steps I’ve taken myself with no prior knowledge and only the /e/ guide to support me when I installed it on my Fairphone myself 2 days ago.
I’m assuming you’re stuck on the same part that stumped me: you have to browse to the folder where you downloaded the adb and fastboot files, you mentioned you put it onto an SD card if I understand correctly?
When pointing the command prompt at a different you start with “cd destination folder”, but if it’s located on a different drive, you need “cd /D destination folder”.
Then you can test if putting “adb devices” in the command terminal while your phone is plugged in (with USB debugging turned on) prompts a response and after that test if inputting “fastboot devices” in the command terminal (while the phone is in fastboot mode) does the same.
It’s important to know these work just fine like @AnotherElk mentioned.
From your explanation it seems you rather struggle with the part beyond “unzip”, which wasn’t very clear for me either (“Do I unzip using the terminal?”).
After I knew adb services and fastboot worked correctly, I unzipped the /e/ file manually (using Winrar) into the same folder where adb and fastboot were located.
I then opened the command terminal, input “cd /D destination folder”, put the phone in fastboot mode and followed the /e/ install guide from there on.
The short version: from the looks of it I think you got stuck on the "unzip " like I did. I unzipped the files manually to the folder where I had placed the adb services and fastboot files.