It depends. There are different types of skin cancers. For melanoma, it can present as mole or pigmented lesions that changes color, grows, ulcerates and bleeds. For squamous cell ca, early stage starts like tiny skin plaques with thick flicky skin that can grow ulcerate with heaved up margins. Basal cell ca may have different forms but check with you physcian if not sure.
Skin growth. There are different types of skin cancer- melanoma, squamous cell, basal cell carcinoma etc. All are presented with skin growths-with different features. Mole that changes- in size ( growing), colors (multi colors), irregular shapes, or with symptoms-itchy, redness, bleeding etc--could be cancerous. Skin growth that is growing or unhealing wound could be cancerous. Dont delay-see a dermatologist.
ABCD's. Remember your abcd's when thinking of melanoma. Look for moles with asymmetry boarders that are irregular color differences within the same mole diameter greater than 6mm also any new mole or old that starts to itch, bleed or ulcerate should be of concern. Another rule is the ugly duckling rule. Which refers to a mole that looks distantly different from the others on your body.
From None to severe! If caught early enough, a skin cancer won't cause any symptoms. If severe it can cause any myriad of symptoms if it has metastasized. Generally skin cancers start and then grow slowly. Once they get big enough, them may itch, hurt, ulcerate and bleed. If you such a lesion, get it checked out, asap.