lessons, lessons, lesssons until you can link turns comfortable with proper form. They will help a ton and you'll learn to control you speed safely. Unless you are doing freestyle, you're unlikely to hurt your knees. Most likely serious injury as a new rider are a broken wrist or head injury if you get out of control or unlucky in a fall. Lessons greatly reduce that.
Buy a helmet. Your noggin is priceless. Knees can be somewhat replaced.
The worst injury I had my first season was my tail bone. Flatbasing down to the lodge for a brew. Got lazy and caught my heel-side edge. Tailbone directly on ice. I skipped the beer and had two shots for major pain relief.