How to use Graph API?

Question

I would like to know the contract structure and pricing structure for using Graph API.

Am I right in understanding that if I sign up for Office365, I can use Graph API?
In that case, which plan to choose to use Graph API?
https://www.microsoft.com/en-ww/microsoft-365/business?market=af#compareProductsRegion

I want to know if there are any other contract structures available.

I read the official document, but it didn't clearly state that you can use Graph API. I'd like to know if this is correct.