How do I auto populate Opportunity, Account auto populated on a record of Custom Object "Project" that is created from Opportunity.

I have create a custom Object "Service Delivery Plan". I want to have a set up where when a check box field (SDP required = true) and (Opportunity Stage = Contracting) then it should create a record of SDP where the Account Name and the Opportunity Name should be auto populated. Could someone please explain me how do I achieve this? TIA

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