When you open a record (not a template), and select the 'Save As MARC' option, or press <F9>, RIMMF will produce a MARC record, based on the instructions that are in the Rda2Marc/A or Rda2Marc/B columns; and write it to the data folder used for your records.
We have begun to set up the Person entity Rda2Marc/A mapping, so you can try this <F9> step with a Person record to see how this works.
We have not done much work with the other FRBR entities, yet; so unless you, yourself, have configured the appropriate RDA2MARC mapping column in the element editor, its most likely that all of the elements in your RDA record will appear in separate 999 fields in the resulting MARC record(since 999 is RIMMF's default field for unmapped elements).
This MARC Export is somewhat experimental in version 1 of RIMMF, but we hope to improve it as time allows.
In any case, if you want to learn more about how the MARC mapping works in RIMMF, please follow this link.