You would define which record you would want to print using Criteria like -
DoCmd.OpenReport "MyReport",acViewNormal,,"[MyField]=Forms!MyForm!MyField"
The last bit is the Criteria and is basically -
[MyField] is the name on the unique fieldname of the record that identifies the record you want to print - it could be the Primary Key.
Forms!MyForm!MyField is the place where the value of MyField is to be found. In this case, On a form called 'MyForm' in a control called 'MyField'
This method assumes that the record has already been selected on a form prior to printing. The Report name here is 'MyReport'.
If the field to be used in the Criteria is on a subform then the code would be different, like -
DoCmd.OpenReport "MyReport",acViewNormal,,"[MyField]=Forms!MyForm!MySubform.Form.MyField"
HTH
Dave E