What are the different types of irons?
Irons are clubs used for accuracy off the tee, or for when there is a shorter distance between where you are and your intended target. There are many different types of iron, starting at a 1-iron, often called the driving iron, and ending up at the 9-iron. The 1-iron has the least loft and the loft gets greater as you go up in the range. In theory, wedges are irons, but they come in a different group of their own elsewhere on the site.
The main thing to learn about irons is that they can be generally grouped into cast irons and forged irons.
Cast irons are usually made of cavity back construction, and are also called perimeter weighted. The head weight is tended to be concentrated on the club face edge, and this provides the player with a larger sweet spot. This is why a cast iron is better for beginners, who have more tendencies to mishit the ball and thus need something more forgiving. But even pros use cast irons, as they like the larger sweet spot and manufacturers are beginning to be able to provide the same advantages of forged clubs with the benefits of cast. Cast irons are made of harder steel than the forged irons so are more durable and consistent as well.
Forged irons do not have any special weight distribution on the club head, meaning that the centre of gravity is located more in the centre of the head. This makes the sweet spot smaller, yet for the lower handicapper, more control is available. This is why lower handicap players prefer forged clubs. If you can hit the ball in the centre of the iron then you will prefer the extra "feel" of a forged iron. This feel comes from the softer steel which constitutes forged irons.
There are also different types of iron club head. The standard golf irons are smaller and the sweet spots are similarly smaller, but for advanced players the extra control that you can get from smaller iron heads is an advantage. Midsize iron club heads combine the advantages of standard and oversize club heads. The sweet spot is bigger than standard and the control is better than with oversized clubs. Oversized club heads have the biggest sweet spots and are thus better for beginners, but they are also more difficult to control, and so better players would not benefit so much from them.
Some irons are now being made from titanium, which makes them a lot lighter than the steel irons. This means that the heads can be larger and more forgiving for beginners, but are also more expensive as the material is more scarce.