Ct of head ystrdy showed sm hole up lft. Doc said indicative of brain cancer. Said it'd be bad if it hasn't always been there. Then left! Next step?

MRI to better. Evaluate. Ct is a good first step, but a contrast enhanced MRI provides much more information about the degree of enhancement, presence of edema, and is optimal for surgical planning if it is in fact a tumor. If tumor detected, make sure to be evaluated for treatment at a high volume academic hospital as outcomes are tied to experience.
You should see a spe. A brain specialist(neurologist or neurosurgeon) should be consulted to check you and guide you further. A brain MRI is often a better test to determine the nature of the lesion that you have, especially if there is any concern that it could be brain tumor.