Start pSX Emulator v1.12.
File > Configuration > Paths tab > make sure for Memory cards it says cards.
Then click the Memory Cards tab > For Slot 1, click the little square button with the 3 dots > Double-click the cards folder to open it > type in whatever you want.bin for the File name (MemcardOne.bin is what I use) > Open > Apply > OK.
Now if you look in the cards folder, you should see MemcardOne.bin
That's your memcard file.