Put a picture on the front, print it on one side of A4, fold it in half. Write inside by hand.
Drag the picture to move it in the frame.
Only if your printer can print right to the edge of the paper. Most leave a thin white margin.
A line or two about the picture, printed at the foot of the back.
Print it at actual size (100%, not “fit to page”) on one side of the paper. Card of 200–250gsm folds well, if your printer takes it.