Hi Tim,
You have some great advise above. The thing that strikes me, however, is you were asking for fairly basic information on block planes. However, some of the advise started in the middle, rather than at the beginning, so I was thinking that maybe it would be OK to give a basic beginning review of the different types of bench planes and a word or two on the block plane. This is not to contradict what is written above, just to give a little more basic information so as to make clearer what is written above.
The first function, historically, of bench planes was starting with rough lumber and getting it to flat smooth lumber that is the right thickness and prepared so that it can be glued up, if need be.
There are three basic functions of bench planes, which are smoothing, flattening, and stock removal. In this description, I will write about Stanley planes because they are so very common, and some of the other companies used similar number to describe the size of the plane, but not all did. For that reason I also list the length of the plane and the width of the iron.
The first step is stock removal to get close to the right thickness, and to start to flatten the lumber. The stock removal plane is the "Fore" Plane, as it is used "fore" any other plane is used. It uses a fairly cambered iron, so as to take off stock fairly quickly and also do some rough flattening. The classic fore plane is the Stanley #6, which is about 18 inches long and takes a 2&3/8" wide iron. A strongly cambered iron takes of stock pretty quickly. The Stanley #5, the "Jack" plane is also used for a "fore" plane by some folks, and works fine, again with a heavily cambered iron. The #5 is 14" long and take a 2" wide iron.
The next step is flattening, and for this a jointer plane is used. It has a pretty long sole, and a mildly cambered iron. The classic jointer planes are the Stanley #7 and the Stanley #8. The #7 is about 22" long, and takes a 2&3/8" wide iron. The #8 is about 24" long, and takes a 2&5/8" wide iron, and is one horse of a plane, it seems significantly heavier than the #7. There are a heck of a lot more #7s than #8s around, so this tells you which one folks generally preferred to use, and the #8s cost more too. These use a mildly cambered iron, and if used to flatten a surface like a bench top, or even something as big as a table top, a lot of folks first go across the width and about a 45 degree angle to the length of the surface. After going over the entire surface from one side, this is normally followed by the same procedure from the other side. The idea is to remove the needed amount of material, and at the same thing to level things out, checking the surface with winding sticks as you go. After it is pretty much the dead flat, the plane is used length wise down the length of the surface to get the surface dead flat. The long length of the sole helps tremendously. The jointer plane is also called a "try" plane, because it is used to "try" the surface and get it dead flat. Stanley also advertised the #6 as a small jointer plane. It could be carried by a carpenter in his tool box more easily than the larger two sizes, and quite a few may have been sold for just that purpose.
The last plane used is the smoothing plane which uses a very slightly cambered iron and it is used to get the lumber smooth and ready to finish, normally you take a very thin shaving. The standard smoothing planes are the Stanley #4 and #3, the ones I have a both about 8&3/4" long. The #4 takes a 2" wide iron and the #3 takes a 1&3/4" wide iron. The other commonly used smoothing plane is the #4&1/2 which is a little longer, and takes a 2&3/8" wide iron. It is typically used on larger surfaces because it takes a wider curling. Much less common and much less commonly used are the Stanley #1 and #2, which are also classed as smoothing planes, but they are pretty small, and the original Stanley planes in those sizes tend to be pricey, the #1, if you find one, will be extremely pricey if the seller knows what he has.
Even in a very extensive Neander shop, however, you don't need all of the variations of sizes. You can get by quite well with one smoother, one jointer, and one fore plane. The best choice as to which one of each of the size options will depend on the size of your work. Some guys, like Steven and Jim, use multiple sizes, but most of us can get by, again, with only one of each.
However, there is another option to having the three common sizes of planes.
That brings us to the jack plane. That size is the one carpenters normally carried, and home handymen, home hobby woodworkers, and maintenance men who had to do carpentry or general woodworking repair work most often had. The #5 is 14" long and uses a 2" wide iron. The other size Jack planes are the #5&1/4 and the #5&1/2, the 5&1/4 being a bit smaller and the #5&1/2 being a bit larger. By far the most common, overwhelmingly, is the #5, which tells you which one was the most generally useful.
If you have the three types of irons for it, heavily cambered, mildly cambered, and slightly cambered, it can be used as a fore plane, a jointer plane, and a smoothing plane. It will not do any one of the thee jobs as well as the dedicated plane, but in skilled hands it can do any of the three jobs to a reasonable extent. I had only a #5 and a block plane for a long time, and used it for everything. Lots of folks did just that because they may have only had the one plane.
That brings us to the difference between bevel up (low angle) planes and bevel down (standard bench planes such as the Stanley Bailey planes) versions. The low angle planes are more of a specialist, doing wonderfully on end grain and for that type of application such as a shooting plane, but pretty prone to tear out if used lengthwise on a board. The standard planes on the other hand are better for planing lengthwise down a board or wooden surface, but not so good on end grain. Thus if your cutting boards are going to have end grain up, you want the low angle plane (I would use a #5) for a standard size cutting board. On the other hand, if your cutting boards are going to have the lumber run lengthwise down the cutting board, the standard bench plane is better. The standard #5 will also be much better for general woodworking.
The above is a short survey of the historical uses of the planes. I use mine for many other tasks.
Finally, "sharp" cover a multitude of sins. If your Stanley Bailey #5 is frighteningly sharp, it can be used for shooting and for end grain work. It won't do as well as a bevel up plane, but it can be used. Because of that critical factor "sharpness," you will need to know about sharpening, and have some sharpening stuff.
For general woodworking, you can use a very sharp #5 for final smoothing up of an edge worked on by a power jointer to clean up chatter marks, just before glue up, etc. You can use it to fine tune doors, etc. to fit. You will use it for lots of things.
Regards,
Stew