Connections and inputs define how your block can connect to other blocks.
Connections define where and when different blocks can connect together. There are four different types of connections:
Output connections and input connections can connect together, and next connections and previous connections can connect together.
You can further restrict which connections can connect by setting connection checks.
And you can customize the shapes of connections using a custom renderer.
An input contains a sequence of fields, and may or may not contain a connection. There are three different types of built-in inputs, which handle the majority of use-cases for Blockly. You can also define custom inputs, which support custom rendering.