[2023] Please Help Me with my Calculations ;-)

It's a resource exchange. You can convert Credits into Coal, or Commander XP into something else.

Typically in conversions like these, there's not a 1:1 ratio as a player is deciding to convert what they don't value (or have an excess of) into what they do value.

Also, there are ships available for whatever resource you would like to use to attain them with.