Biddlecombe's Art of Rigging is an extremely valuable book. In most respects it's a revised version of David Steel's Elements of Rigging, Sailmaking, and Seamanship (which dates from the 1790s), updated to the mid-nineteenth century. Biddlecombe is particularly useful for such vessels as packet ships and early clippers - though the latter introduced some variations that he doesn't cover. And later clippers (e.g., the Cutty Sark), with their wire standing rigging, iron yard trusses, and other "modernized" gear, introduced still more.
The "progressive method of rigging ships" is, if I remember correctly, borrowed almost directly from the earlier Steel book. It makes a good start for figuring out how to rig a model. Some of the specific details aren't particularly relevant to the modeler (there's no need for a modeler to lash boat oars to the ship's shrouds for men to stand on while they're rigging the ratlines), but it provides a good, solid basis for an understanding of how rigging works.
Seizing is the act of wrapping a piece of fine line around a pair of heavier lines, as a means of holding them together. In this particular case we're talking about "seizing an eye" - that is, forming a loop of fixed size in a piece of heavy line.
The procedure for rigging a pair of shrouds, in a real ship, goes something like this: 1. Seize a deadeye into one end of the line. (To do that, loop the line around the deadeye, hold the ends of the line together, and wind a piece of finer line around them. Each end of the fine line gets tucked under the last turn of itself, between the parts of the heavy line.) In the case of a shroud seized around a deadeye, it's normal during most periods to use a "triple seizing" - that is, to make three separate seizings, spaced a foot or so apart. (In the Cutty Sark, if I remember right, the seizings are painted white to give them a neat appearance.)
2. Run the other end of the heavy line (the shroud) up the mast (not mask, by the way; I imagine that was a typo), through the "lubber hole" in the top, around the masthead from front to back, and down again. The first pair to be rigged is the foremost one on the starboard side of the ship.
3. Seize a second deadeye into the remaining end of the line. (That part of the line is now the second shroud.)
4. Seize the bight formed by the two shrouds snugly around the masthead. (For this job a single seizing is the norm. In a model you can seize the two shrouds together a couple of inches below the masthead, then slide the seizing up until the whole setup is snug.)
5. Rig the lanyards between the deadeye pairs. Start by tying a Matthew Walker knot in the bitter end of the lanyard, so the line can't slip through the hole in the deadeye. (In a model, don't try the Matthew Walker knot. Just tie a reef knot - aka square knot - with a couple of extra turns in it, to make it nice and fat.) Then pass the lanyard through the six holes in the two deadeyes. Any decent diagram will show the sequence. (You'll notice, even on a small-scale model, an interesting phenomenon: the lanyard runs freely through the two deadeyes, and the distance between the deadeyes can be adjusted quite easily, until you rig the lanyard through that last hole. Then the whole system goes rigid. If you want to adjust the spacing after that, you have to pull the lanyard through the holes one at a time - sort of like adjusting the laces on your shoes.) There are several ways of securing the hauling end of the lanyard; the most common during most periods seems to have been to "expend it in half-hitches" - i.e., to simply knot it several times around the shroud just above the upper deadeye.
When you're done, the upper deadeyes in the gang should all lie in a nice, straight line parallel to the channel (or, in the case of the Cutty Sark, the rail to which the lower deadeyes are attached).
In a model, the challenge is to get those upper deadeyes in line while simultaneously keeping all the shrouds taut. (They need to be really taut; the rest of the rigging process depends on them. In the real ship, the shrouds are a key component in the propulsion system. The wind fills the sails, the sails pull on the yards and masts, and the masts, by means of the shrouds, pull the ship.) Unfortunately there's no real secret to doing it, other than practice - and practice, believe me, is no guarantee that you won't screw up occasionally and have to start a shroud over. The three little tricks I mentioned earlier in this thread (leaving the deadeye seizings to be adjusted late in the process, seizing the bight around the masthead after the deadeyes are set up, and shoving the bolster under the bights last of all) help a little, but there's no getting around the fact that this is one of the trickiest jobs in rigging a ship model. It's made worse by the fact that, by definition, the shrouds almost have to be among the first lines you rig - before you get much practice on anything simpler. (This is one of the many reasons why Olde Phogies like me urge newcomers to start with something that doesn't have many shrouds.) The good news is that once you've rigged the shrouds the rest of the rigging gets easier. And a nicely-set up set of shrouds and ratlines is a real asset to any ship model.
Hope that helps a little. Good luck.