Open the .exe file and select your Japanese Mother 3 rom, and it will do the rest! You will be able to play the lost Mother game that never made it out of Japan in glorious English. Most of all though, have fun.
I may try the new ram site, and download more RAM to my Switch. Not sure if ddr3 is the right ram
for it tho. Edit- no it uses floppy Ram, just like @AncientBoi