Is it true that nodular melanomas start out as a very small pimple then grow raised rapidly?

That is often the case. Some melanomas begin as small flat patches then they grow very fast as they become biologically more aggressive; first they may grow inward (early invasion of underlying skin tissue) but later the growth becomes also exophytic (growing outward above the surface of the skin and thus producing a small "nodule"). Other melanomas may arise within flat or nodular nevi (moles)