How To You Prepare 250ml 15m Solution Of Naco3 In A Volumetric Flask

How to you prepare 250ml, 15M solution of NaCO3 in a volumetric flask? Do we presume a solvent ie H20–Na2CO3 + H2O — 2NaOH + H2O + CO3but then you have to presume volumes and concentrations as well. i dont understand how to explain, also becuase in volumetric we wont be diluting it will we. im confused