There are many different types of skin cancer, however there are three main types that account for the majority of all skin cancers; squamous cell carcinoma (SCCa), basal cell cancer, and melanoma. Almost all skin cancers form in the outermost layer of the skin (epidermis) and thus are typically first identified by sight. The fact that cancers form in the outermost layer of the skin is due in part to the fact that the epidermis is exposed to the most environmental factors. In fact the UV light from sunlight is commonly thought to be the number one risk factor for the development of skin cancers. However there are multiple other factors that can be involved such as smoking history, skin color, age, exposure to ionizing radiation, exposure to environmental carcinogens, immune status, and even genetics (some genetic syndromes put people at a much higher risk of developing a skin cancer). For these reasons, and particularly with your history of frequent sun burns as a child, if you have abnormal looking moles or freckles, especially if they are getting larger, I would get them checked out by a physician. The best place to start is with a dermatologist
. I hope that this is helpful, and I wish you all the best.