Start in Pages with four blank pages in the Page Layout section.
The first document page will be your cover, or front, and the second document page will be the back of the card. After these are finished to your satisfaction, you will need to flip the pictures and text boxes both vertically and horizontally. When the sheet is folded, they will be right side up with the top at the fold. Be sure you have the text below or above the picture where you want it. I found that I had to leave the page and come back to it before I could flip them. (In Word, flipping seems to be impossible unless you can change it into a drawing. So save it, open it in Preview and flip your pages there. You might want to customize your tool bar from the View Menu, or flip it from the Tools Menu.) Use the Option key with the flip to do only that page.
The third document page will be the first inside page of the card. The fourth document page will be the second inside page of the card. These do not need to be flipped. When you are happy with them, go to the Print menu, and where it says Copies and Pages, click to show Layout. Where it says Pages per Sheet, check “4” and leave the Layout Direction on the first setting. Now you can save your file as a PDF to look at it, or go ahead and print it, fold it, and you are finished!