Adding initial content for "Handling Data - Blocks" section (#418)

Author: bendbennett

website/docs/plugin/framework/handling-data/blocks.mdx

@@ -5,3 +5,27 @@ description: >-
 ---
 
 # Blocks
+
+A block is a container for other content:
+
+```hcl
+resource "aws_instance" "example" {
+  ami = "abc123"
+
+  network_interface {
+    # ...
+  }
+}
+```
+
+A block has a type (resource in this example). Each block type defines how many labels must follow the type keyword. The resource block type expects two labels, which are aws_instance and example in the example above. A particular block type may have any number of required labels, or it may require none as with the nested network_interface block type.
+
+After the block type keyword and any labels, the block body is delimited by the { and } characters. Within the block body, further arguments and blocks may be nested, creating a hierarchy of blocks and their associated arguments.
+
+The Terraform language uses a limited number of top-level block types, which are blocks that can appear outside of any other block in a configuration file. Most of Terraform's features (including resources, input variables, output values, data sources, etc.) are implemented as top-level blocks.
+
+## List, Set and Single Nested Blocks
+
+Wherever possible, the usage of [nested attributes](/plugin/framework/handling-data/terraform-concepts#nested-attributes) is preferred.
+
+The three options for [nested blocks](/plugin/framework/handling-data/terraform-concepts#nested-blocks) are `ListNestedBlock`, `SetNestedBlock` and `SingleNestedBlock`.