Step 4: Cutting, Folding and Gluing/Taping Pepakura.
The dashed lines indicate you'll need to make a mountain fold along that line. To make a mountain fold: Hold one side of the line in your hand(line facing up), and fold the other side down. from a side view with the line facing up, the fold resembles a mountain peak.
The dot-dash lines indicate a valley fold. Keeping the line face up and one side in your hand, fold the other side down. Again, from the side, this fold resembles a valley, with the line facing up at the bottom of it.
The solid lines show where you need to cut.
I find it's more productive to cut all your pieces out first, and then get to folding and gluing/taping.
To aid folding the pieces, line a ruler's edge up with the line. Then press something dull like a dry pen over it a time or two, to crush the paper in. This makes folds much more exact. If you can't find a dry pen, a working one will do, just make sure you indicate what a line is before you black it out solid. I mark a small "V" pointing at a valley fold line. When folding the pieces, you don't have to fold the pieces really far out, this is more of a creasing process.
So one you have the folds made to all the pieces, you need to join them. Pick up a folded piece, and take note of some of the numbers that are printed on it. Now take a look at the numbers on the other pieces. When you find two of the same numbers, you've found two pieces that need to be joined. This is very simple. One of those numbers will have a folded flap under it. What you will do is take the numbered edge that doesn't have a flap, and slide it up to the fold line of the numbered flap, putting the flap under the other piece. I have a picture to clarify this. To keep em together, put some super glue on the flap or tape both sides of the joint. You'll want to tape both sides to give some strength to the completed piece.
Repeat the process until you have a completed 3D piece. As to how many full pieces you should assemble before resining, it's up to you. Think about how much space you have to store the pieces while they cure. For example, if you only have the space to store two arms, you'd be better off resining them, and moving on to cutting and folding other pieces as the arms cure. You'll develop a feel for this as you work with the costume.