What if the colonoscopy shows something abnormal?

Diagnosis/treatment. At colonoscopy most visible abnormalities are either definitively diagnosed via sampling (biopsy) or removed completely also for diagnosis that includes the treatment. Some findings, eg cancer, need definitive treatment via other modes (for example but not limited to surgery).
Chat afterwards. Generally, your doc will have a brief chat with you after you wake up from sedation and quickly review what they found. At that time they'll communicate any abnormal findings, whether a biopsy was taken and what they expect to find. They should also send you a home with a printed report (or you might get it in the mail).
Biopsy taken. If something unusual shows up during a colonoscopy, a biopsy (tissue sample) will be taken. This will be evaluated by a pathologist. Then you will be advised what if anything further needs to be done.