To cover a ceiling with tin (steel, actually) you need panels for the field and cornice pieces to bridge the junction between ceiling and wall. The good news is that, once you provide room measurements and — configuration, manufacturers will calculate for you how many of the 2-by-2-foot panels and 4-foot cornice pieces you actually need. That includes cornice pieces cut to fit together tightly: At inside corners, one piece will be coped (cut at an angle and shaped to hug the curves of the adjoining piece) and at outside corners both pieces will be mitered to meet at a point.
The steel comes either powder coated or bare; the former is meant to be left looking like metal (and is colored in different finishes), while the latter is for painting. Traditionally, tin ceilings were painted; if you have any trepidation about installing the ceiling neatly, you should probably plan to go that route. That way, you can caulk and paint over mistakes. If you leave the metal showing, you can still cover imperfect joints with clear caulk and metallic touch-up paint, but these spots will be more visible. Keep in mind, also, that the patterns on these ceilings have a repeat; a smaller repeat is better for a smaller room.
The metal used for the panels is heavy—if you hang them directly off of drywall or plaster the nails will pull out. So first you'll need to cover the ceiling with plywood to create a secure nailing surface. This is the most difficult part of the job: finding the joists and then raising and screwing plywood sheets to them. Think about layout before you start putting up panels. A row of panels should be centered over the entry to the room, and the joints between panels should overlap in such a way that cut edges face away from the room's entry. This will make the ceiling look neater to someone walking through the door.
Once you have your plywood up and your layout scheme established, nailing up the metal—especially if you rent yourself a brad nailer and compressor to alleviate the tiresome work of hammering overhead—is just a matter of finessing the panels and cornice pieces into place.