I am not a big blocking expert because I have knit with acrylic a lot and most of the patterns I've made end with "do not block". Blocking works on animal fibers the best although even acrylics and cotton can be wet blocked and I think it makes them look a little nicer, but there is no big change. You can also just wash and dry acrylic yarns (according to label directions) to finish them up a bit.
Blocking is something you do to a finished knitting project to flatten (you don't want to flatten some kinds of stitches though), and shape it and to even out the stitches, it makes your item look more professional when done, and it works miracles on lace.
People used to use an iron a lot and it can still be done with an iron utilizing steam, either with a damp cloth or a steam iron. Some folks use some sort of a steamer that is not an iron. Before you try it you should read more about steam blocking somewhere.
Here is a site that tells about cold water blocking. This is a good technique and works for a lot of yarns.
Cold Water Blocking
Sometimes when I have blocked something I am a little more relaxed about it and just lay the item out, spray it (or I might wash it and spin dry it or roll it in a towel), and then smooth it with my hand, pat it around and nudge it into the shape I want. I don't necessarily do all the pinning and all, although it is great to do it that way. Sometimes I use stainless steel table knives to lay along the edge of something I want to lend a little more encouragement to in the way of flattening along the edge, or to hold a position I put it in. I go back and look at how the project is drying from time to time and may make adjustments.
If you are making a sweater in pieces you can block the pieces before you sew it together. If you make it all in one piece you can just block the whole thing at once. You can also block scarves, shawls and anything else really.
You can use any flat surface that is safe from pets, etc. to do blocking on. A table with towels on it will work, or a bed.
We had a thread about this recently and the truth came out that many of us don't bother to block things and are still happy with our work. So it is optional, sort of. LOL I think lace really needs it.