"Not enough space left to complete backup" on 4GB empty memory stick?

I have been exploring how to make a backup so that if my computer dies I will have some record (I assume that is what it means) to put on a replacement computer to make it similar to the one I am using now

I use Firefox so tried their FEBE extension ....
FEBE Firefox Extension
but that didn't seem what I wanted

I then tried Tweaking.com Registry Backup as I already have their Windows Repair Pro which I was advised to install in case I ever have problems in the future with something going wrong but have not had to use (yet?) ....
Registry Backup
but didn't understand how I could get that on to a new computer.

So, I uninstalled both of those and have been trying to make a backup onto a memory stick but am running into problems that I will do my best to explain clearly.

I have tried two new 4GB memory sticks and followed the advice in Control Panel, Backup and Restore.

The Start, Computer screen confirms that Drive I (the memory stick) has 3.85GB free before I start.

All starts well but after a while I get the following message "The disk that your backups are being saved on doesn't have enough free space" and also says that I only have 1.39MB free of the 3.8GB.

So I found a video and tried to follow the instructions carefully ....
https://www.youtube.com/watch?v=ZRdkLClj5rQ
and did so until 2.40 in. The previous steps I followed were fine but I simply could not find the Windows Backup file.

I followed the instructions to delete that backup and tried again. I then tried twice with a different new 4GB memory stick from a different supplier but had the same result.

At that point I came here and looked through the Tutorials but I am thoroughly confused and lost.

Please could some kind person help me make a backup?

(Also, I would really appreciate an explanation of what it actually will do if/when I pop the memory stick into a new computer once this one eventually dies)?

All and any help greatly appreciated please

Best to make a full copy (image) of your hard drive, to recover. The Windows backup only backs up certain files. You are still left to reinstall most everything (including Windows). The Marcrium Reflect (a UK company), free version, will do nicely. But, you need something more than a disc or flash drive. A USB connected hard drive would probably be best.
Macrium Software

Thankyou ... I have read the link and it seems I will have to learn a lot more to be able to understand it fully at the moment but it may well be the way for me to go once I have conquered (simple) backups on my own computer.