Whenever I walk up stairs orwork out my left knee clicks and feels like its grinding. Is this a major problem?

Patellofemoral Syndr. Pf syndrome is the most common cause of non-traumatic knee pain (and clicking) and is especially common in young females. It is caused by an imbalance between the knee hinge and the muscles of the thigh, the quadriceps, and often develops after a recent period of increased physical activity like sports. Fortunately, it's easily and effectively treatable with physical therapy so go get some!
Chondromalcia of the. Patella, it is not a major problem but should be treated.
Not major but. You should take of it. Most likely chondromalcia of the patella.