Planks are a hold exercise, not a rep exercise. You can be on your hands or on your elbows/forearms, whichever is most comfortable for your body and your goals. Planks are something you can do every day for 1-minute, but working up to that first initial minute can feel difficult. Start with 15-second to 30-second holds; take a break, lower to your knees, have a rest, and rise up to finish the remaining count. Work up to 1 minute holds that you can incorporate into your workout routine.