It's right there, on the announcement page:
Use mdconfig(8). Check the EXAMPLE section near the end. It shows all you need to do to create and mount a file-backed device. When that's done, you simply copy the .txz files you want and unmount it.Please, can you tell me how can I make/create a .img of the FreeBSD.
memstick.img is right for me, but I need to add some packages to the memstick.img. How can I do ?
Use mdconfig(8). Check the EXAMPLE section near the end. It shows all you need to do to create and mount a file-backed device. When that's done, you simply copy the .txz files you want and unmount it.