They are talking about something like this:
There are certain ones that come with dividers to make the crate smaller for when your dog is a puppy but allows you to move the divider as they grow so you do not have to keep buying new crates.
It is a wonderful wonderful thing. Helps keep them out of mischieve when you are not able to watch over them and for when you are gone out of the house and at night time. Your pup will love it if you train her the right way, many of the dogs on the board go into their crate willingly just to take naps.
Also, when your pup is so young, for potty training purposes, many people have their dog in there at all times except for play times, and outside times, this way there is no time for the pup to go potty in the house.