That should probably be multivitamin
supplements which do not have any dangers ( very safe) except of course their formulations includes unknown substances inside.
As for your severe knee pain
you are actually having increased secretion of acetic acid
in your knee joint synovial spaces which is responsible for the pain since you were probably not use to doing exercises before. A few days to weeks of stamina or endurance will get your system adapted. I don't think you need any food supplements. Just eat normally, take protein rich and energy rich meals that can support the anaerobic metabolism
that is going on in your knees during and after exercising.
If pain is severe take some analgesics to relief.
Hope this helps and remember exercising is very important for your system to function normally, so you have to keep up the keeping fit