If you have a large piece, pinning it down helps immensely. There always comes that moment when we cast off the last row, and tie off the last stitch.
There are actual knitted fabric blocking boards you can buy for this purpose; often I use my ironing board or a large atlas or other book on which to lay my fabrics.
When you block something, it reduces curling, matches pieces to one another, (as when knitting a sweater), it makes your edges straighter, or it shows off the patterning (as in dishcloths; they "pop out", so to speak). Any garment, dishcloth, afghan blocks, and many other projects require you to block your finished piece.
As with anything, all good things must come to an end, and so it is with whatever we are knitting.
Now what?
Well, with some projects, nothing else is required.

If you want to be taken seriously as a knitter who gives gifts or sells knitting at craft venues, then your finished creations must look their very best. Once you finish knitting, you can begin wearing immediately.
So, let us take a look at finishing requirements for our knitting. Again, pin the garment down and using a steam iron, spray with steam.
Knitting is so much fun, I could spend all my waking hours with yarn and needles, just designing away.

Don't touch the fabric directly with the iron.
With other projects, however, there are some definite finishing techniques that you should apply in order for your pattern to look professional. Never wring or twist the fabric. One is by soaking the knitted piece in water; squeezing out excess moisture gently, by rolling into a towel, then laying flat to dry.
Another method is by steaming. Certain projects, such as scarfs don't require any real blocking.
Any good knitting pattern should give you blocking advice; and be sure to finish each project this way.

There are a number of steps to take to ensure that our knitted creations look their very best!
The first thing to consider is blocking.
There are different ways to block. Leave it to dry completely.
Remember to leave your fabric alone once it's wet, and let it dry Flax fabric naturally off in it's own little corner of the world. There are specific ways to achieve this. The top of the clothes dryer is another good option. It's not exactly knitting, yet, it will assure you that what you knit will look fantastic!