BRRR Method Example

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Question on understanding the BRRR method from a high level. For example, and I'll make it very basic and I understand it's more complex than this but, if I buy a house for 50k, put 20k into the rehab, and say it's done with cash so all in cash I'm at 70k. And the ARV is supposedly 100k. When I go to refinance after 6 months, and the bank gives me a 70% LTV (so 70k loan), here is where my questions start:

Do I now have 30k in equity in this house and the bank realizes that and can finance the 70k and make monthly payments on that?

I get a little lost on how exactly the refinancing works. Any explanation will help, if I need to clarify or provide additional information let me know please. I appreciate it!