Joe, I'm not familiar with this particular name brand, but assuming this is a cement board, often coming in 3'X5' sheets.
If so, there's normally nothing done to the joints except to butt them as close as you can, and the thinset mortar used to adhere the tile is pressed into the joints during the tile process. Personally, I mix a little thinset, or use a caulking such as Mortar Patch or a polyurethane concrete caulking, and run a bead of this down the edge of the first sheet I installed, then place the adjoining sheet. This squeezes the sealant to completely fill the gaps.
As far as what to do at the base depends on what your base is. If the base is a formed fiberglass pan it will have a flange on it that lays against the studding. Put a bead of sealant on the flange, then install your permaboard in front, so that it overlaps the flange.