Formatting your memory card will erase all information, in other words your photographs, from the card. It’s a function performed in your camera and it’s important you know that it will erase all of your photographs. It is “healthier” for your memory card if you format regularly, but only after your images are safely stored elsewhere.
Using the delete function will also erase your images, however, it does not erase “picture file information residue” which is left on the card. Formatting removes this residue and helps prolong the problem free use of your memory card.
“Arrow up” to Format and pressing the Ok button will initiate the process. It’s very quick, usually.