To all the fit people! Help me join your ranks =)

hey everyone! so I'm 5'3 and 170 lbs. about 40 lbs overweight. I've reached the point in my life where I want to get back to being fit because I know that I'll look a thousand times better and I'll feel better and most importantly, I'll live a healthier life. I have a gym subscription but I can't go everyday because of school/work/commute. I wanted to take up running, but I'm worried about the damage it might do to my knees. my left knee already hurts a bit... maybe because of my weight. so any advice regarding diet/exercise? how often and what types? ALSO, is there a 'proper way' to run?
To all the fit people! Help me join your ranks =)
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