How do they work? Well, they are just like AutoCAD blocks. They have lines, arcs, shapes, or whatever. They can also have fills built into them. Or you can just leave the blocks with linework on layers, or on the same layer. Use them however you need, it’s up to you.
If you have a block in a file that has been used more than once you can quickly stylize them. Edit the block, stylize it, and there you go. Every instance of that block will be rendered the same way, right away. It is a great way to get a lot of content into your drawing, and to get it done quickly. Each block can be scaled and rotated individually. But they are all stylized the same.
You can search for blocks in a file by filters. These filters will display a list of based on block type, name, saved blocks, blocks in use, and other criteria. Any block in use in a file can be exported to a block library. This library can exist on your machine or on a network.
As you can see, Impression blocks work very similarly to blocks in AutoCAD. Give them a try, they can and will save you time and effort.