Blocking, by definition, is taking a piece of knitted material, wet it in some way, and then pinning it to shape and allowing it to dry.
If you have never blocked a piece of knitting try this. Knit up two identical swatches about 4 inches square. After knitting them take one piece, gently wash it and then lay it out, pin it to shape and let it dry. Leave the other piece as is. After the first piece has dried compare the two pieces. You should see some interesting results.
The pictures shown here are of a gauge swatch that I knitted before continuing on with a sweater for my son. The yarn is a silk and wool blend. The pictures show you the initial dry piece after it came off the needle; the piece wet and starting to be blocked and the final dry, blocked piece. I hope you will see how blocking has affected this material. The material itself is much softer after being washed, although you won't get a sense of that from the pictures. What you will notice is how the piece now lays flat and you can imagine how much easier it will be to sew when the pieces are completely knitted.
Blocking does a few things. First, it allows the fibers in the knitted fabric to open up. Often knitted work will "bloom" after wetting. Uneven stitches become more regular, a lovely halo appears and suddenly a pattern that was difficult to see opens up and shows the beauty of your work. Stockinette stitch edges that curl in so badly start to behave a bit better making it easier to sew seams. Blocking allows you to shape the pieces to match the pattern schematic and you can actually make a small piece a little bit bigger or improve the shape.
Not every fiber can be successfully blocked. No matter how much you try to block one hundred percent acrylic it really will not benefit from being blocked. However, most animal or plant fibers will benefit from blocking. To test the yarn you are using, take the time to do a gauge swatch and wash it as you expect to wash the finished sweater and block it before knitting your garment. This should be done every time you begin a project. Treating the swatch as you intend to treat the finished project allows you to see if a yarn will shrink or grow, whether colors will run and how a pattern will benefit from blocking.
To block out your piece of knitting you will need water, non rusting pins, a ruler and a surface to which you can pin your work. I use the carpet but you can purchase blocking boards for very little money or make your own.
There are basically three kinds of blocking, wet, steam, and spray blocking. Wet blocking is where you put your knitted pieces into a basin of water, get the pieces completely wet and then block them out. Steam blocking is where you pin the pieces out to the desired size and then using an iron, steam the pieces. Finally spray blocking is where you pin the pieces to size when they are dry and then spray them to wet them and then allowing them dry again.
In wet blocking each piece is placed in a basin of water. Usually a soap such as "Eucalan" is used to "wash" the pieces of any debris, hand oil etc. The water is gently squeezed out of the material, being careful not to agitate the material in any way to avoid felting (shrinking). The pieces are rolled in towels and excess water is squeezed out. The pieces are then laid out onto a blocking board or towels on a surface such as a carpet. Using the schematic provided in the pattern, pieces are gently shaped to the size in the pattern and pins are placed at roughly one inch intervals around each piece. The knitting is then left to dry completely.
Spray blocking is similar to wet blocking but instead of wetting the fabric first, you will place the pieces on a blocking board or other hard surface and pin to the desired shape. Pieces are them sprayed with water until they are wet and then allowed to dry.
Steam blocking can be tricky and of all the methods the most care should be taken with this method. The pieces are laid out to the correct dimensions and then, using a steam iron, steamed. Some fabric should be placed between the knitted item and the steam iron - such as a cotton cloth. Then, without pressing the iron onto the fabric, steam should be allowed to penetrate the knitting. It is then left to dry.
Please try blocking your knitting and let us know your results.