Tanning, the sun, skin cancer and moles?

okay well i have quite a few of the beauty marks,
or moles whatever you want to call them,
and stuff about skin cancer always makes me worried,

i may have got like two or three more,
but ever since i was small i had them so i didnt pay much attention to them, how do you knoww if its skin cancer? or whatever,
like when i go out into the sun i use lotions and stuff..