First of all, I am sorry to hear that you are dealing with a diagnosis of melanoma. As you know, melanoma is a fairly aggressive form of skin cancer but it can, fortunately, be treated well if it is detected early.
Usually the diagnosis of melanoma begins when a suspicious mole or dark spot on the skin is biopsied or removed and the pathologist
determines, after looking at the sample under the microscope, that it is melanoma. When this occurs, the next step is usually to go back to the site of where the spot was removed and perform an additional surgical removal of additional tissue.
This "wider surgical resection" as it is known is important because melanoma has a way of growing small tentacles out from the central spot. Tentacles can lead to recurrence of metastasis of the melanoma, and removing more tissue from around the spot once the melanoma diagnosis has been confirmed is known to improve cure rates of the cancer.
It is also common to look at lymph nodes that drain the region where the melanoma was found, as these are common sites for metastatis. Once the excision has been performed and the lymph nodes have been examined, you should talk to your cancer doctors
who will discuss with you whether further treatment or workup will be needed, as this obviously depends on what is found at these stages.