2years ago an mri showed meniscus tear it wasn't treated at all and now knee is swelled and is extremely painful can't stand on it what can i do,wrong?

Quick fix and more: See an orthopedic surgeon or a physiatrist. They can evaluate the knee. If appropriate, they can drain the fluid and that will give you some immediate relief. Use ice and a compression wrap which will also reduce the pain a bit. Use a cane or crutches so that you take some weight off the affected leg and try to walk without stressing the other leg or your back! But see the Doc, get a diagnosis.