There are many kinds of blocks with unique behavior

Blocks can be placed and mostly are cube-shaped, but some have different shapes/sizes, some placeable blocks are also items and some blocks have unique properties, like:

• Luminosity
• Immunity to explosion/damage
• Harms entities (mobs and special "things", such as primed tnt, an armor stand, a fired arrow...)
• Blocks that become a entity (like tnt, when primed becomes a entity, or an armor stand/minecart when placed)
• Blocks exclusive to creative
• Blocks with their own interface
• Blocks that do not have a interface but can be interacted with
• More...

A block is what you need to place to build things, like (i dare you if you have minecraft) to build a palace