I am going to take you through the process with some photos and explain each photo or step.  Here I am showing one of my Mystery Batts still rolled up and starting to pull from the center of the rolled up batt.

 Still pulling out from the center of the batt in a thin stream.  To do this you hold the batt firmly at the end of the roll and then gently pull the fibers out from the end of the batt through your opening in the hand holding the batt.

 Here I show the now roving or sliver being in a long stream and I have been pulling it into a box.  You can also use a basket or a large bag to put the sliver into after you draft it out from the batt.

 Here is the finished product from the Mystery Batt.  To do this with maller batts of a small drum carder or hand carder you can layer the batts before rolling them up and then draft them out to give you a longer continuous spinning roving.