How to approach being accepted into PhD lab group verbally while explaining grades
(I see you are from New York) In the US, in most fields, it isn't typically possible for a professor to &quot;admit&quot; a student to a doctoral program and you must go through a process of application and evaluation. It is unlikely that such a process can be entirely bypassed, though having a sponsor can be helpful. You can ask them what your next steps should be.
Unless your field is an exception, you need to write a good application, including letters of recommendation that assure any evaluator of your potential for success.
Don't spend a lot of time apologizing for poor grades, but emphasize the positive. What is it that makes you a good candidate? Make sure you have letters that attest to that. Depending on possible regulations, this professor might be a letter writer.