The outside skin of my penis has a red mark on that is itchy and dry. Feels like the skin is dry any cracking. What can it be? How can I treat it?

Many possibilities. There many causes of genital area skin rash -- too many possibilities to even guess based on this information. The large majority of genital rashes are not STDs and most are not serious or dangerous health problems. See your doctor if it continues of if you remain concerned.