I had an mri of my knee and on the results it said fibrillation and low-grade partial-thickness fissuring of the articular cartilage over the patellar facets and superior margin of the trochlear groove. what does that mean in simple terms?

While I personally never received report of fibrillation my patients' knee pathology, it appears to be a subtle sign of cartilage damage. Fissuring is an actual crack but in your case it is superficial and doesn't go all the way down to bone. Since you have impaired knee cartilage at an early age, you should consult an orthopedic surgeon to evaluate your situation&advise you how to more damage