Your results mean that you have tested positive for having a high risk HPV strain (HPV16 or HPV18 are the ones that cause cervical cell changes) and that has caused some cell changes.
They haven't specified how severe the changes are (CIN1 being mild, CIN2 moderate and CIN3 severe) but I believe this is normal as I experienced the same when I found out I had CIN3. I worked out I must have severe changes because the time frame for appointments etc was short compared to only CIN1 which I had several years earlier.
They don't tend to treat CIN1 as far as I'm aware so the fact they are booking you in for treatment suggests either CIN2 or CIN3 but I could be wrong; I'd give them a call and see if they can give you more info if you are concerned. They will be able to explain in full when you have the appointment though.
The purpose of the LLETZ is to take away the 'nasty' cells that have changed due to HPV, which should help your body to fight off any any remaining HPV and prevent anything more serious.
Good luck with it all, I had LLETZ a week ago and it isn't as bad as I'd built it up to be in my head. These changes are surprisingly common and treatment successful in most cases.
Good luck with it.