Hi! If your drawing is sprayed with workable fixative, and all extra charcoal and eraser dust has been blown off of it or shaken off of it, that's where you start. I recommend transporting the drawing flat, between two sheets of cardboard, taped in secure, with a protective cover sheet over it.
(2) identical pieces of stiff cardboard, mat board, or foamcore board that are at least an inch longer and an inch wider than your drawing to sandwich around the drawing in a way where the drawing will not shift around.
(1) roll of masking tape (aka artist tape)
(1) roll of wide clear cellophane packing tape, like what's used to seal a big box for shipping.
How to make your protective portfolio folder: Use the clear, wide packing tape to make a binding along the long side of the cardboard, basically making it into a big folder. Put the clear tape on both the inside and outside edge of the binding (making sure it has room to hinge open and closed) so no sticky tape is exposed, even when the folder is open. Place your drawing inside with the cover sheet over it. If there is extra paper surface that's not part of your drawing that's a great place to carefully apply small pieces of masking tape to affix the corners or edges of the drawing to the inside of the folder. You can also tape down the cover sheet. Just make sure the masking tape doesn't touch the surface of your drawing. You'll need a way to secure the big folder closed too. A big rubber band might work, or masking tape all around the edges. It depends on the conditions under which the art is being transported and whether you intend to open and close it lots to show or work on it or not.
I hope this helps! Let me know if you have other questions. Happy drawing!