The jigsaw block has been a recent block added in the 1.14 update. It is a very mysterious block used for technical purposes to generate structures. In the recent 1.16 snapshots, the block received some updates along with a new texture. In this post, I will explain each setting and how to use it. Also, the jigsaw block is used to generate structures saved in files. This means it's possible to create your own structures and save them with structure blocks. With the jigsaw blocks, you can then generate your own random structures!
SECTION 1 - STRUCTURE BLOCKS
Structure blocks are a feature that allows you to save structures and load them. You can load naturally generated structures too. For specific info on structure blocks, recommend going to the Minecraft wiki.
SECTION 2 - JIGSAW SETTINGS
To obtain a jigsaw block you will have to use commands as it is not in the creative inventory. The command (/give @p jigsaw) can be used to give yourself one. You can open the jigsaw block to enter some parameters.
This setting will tell the block which folder of structures to choose from(bastion/bridges/[blah]).
The name of the jigsaw block will only connect to other jigsaw blocks with the same name(for aligning structures)
This setting is used for the name of the structure to generate.
This is the block that the jigsaw block turns into once the entire structure has been generated.
This one I don't really know about...
GENERATE & LEVELS
The generate button will generate the next structure piece after the jigsaw block. It will continue generating the next structure's jigsaw block for x amount of layers.