I had a Colposcopy and also a Loop Diathermy about 4 years ago.
I can't say it was a pleasant experience. It was a while ago, but from what I remember, the cervix was first stained with a dye and then anaesthetised and the doctor viewed the area through the Colposcope, which I could also see on a TV monitor, then a cortorising loop was used to scrape and burn away the abnormal cells.
I was told to take 2 days off work after the procedure and had a little mild pain, a bit like period pain. I also had a horrible brown, metallic smelling dishcharge for about 2 weeks.
I returned about 2 weeks later for the lab results, where some of the cells were tested for Cancer, fortunately, these did not appear to be cancerous. I then had to go for a follow up smear test about 6 months later, to check there were no more abnormal cells.
The whole procedure lasted about 30-40 minutes and wasn't painful, just uncomfortable.