Introduction: Devnet & Testnet

chapters/introduction/lab/content/explorer/devnet_testnet.md

@@ -0,0 +1,21 @@
+# Devnet & Testnet Blockchain
+
+While developing applications, there is a need for a development/testing blockchain.
+
+Inspect:
+* [MultiversX Testnet Explorer](https://testnet-explorer.multiversx.com/)
+* [MultiversX Devnnet Explorer](https://devnet-explorer.multiversx.com/)
+* [Goerli Ethereum Testnet Explorer](https://goerli.etherscan.io/)
+* [Sepolia Ethereum Testnet Explorer](https://sepolia.etherscan.io/)
+
+What differences can you observe?
+
+These blockchains offer the `Faucet` option where you can mint blockchain tokens (eGLD, ETH, etc.).
+This way the development is easier for the community.
+
+---
+**NOTE**
+
+All the tokens are "fake" tokens. They are only used to mock the real tokens on the Mainnet.
+
+---

chapters/introduction/lab/content/explorer/observers.md

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+# Observers
+
+Observers are a type of nodes that `don't participate in the consensus` but keep a peer-to-peer communication with the rest of the blockchain.
+They are usually used to see the communication between nodes (ex: debugging). 
+
+Let's filter the nodes to see only the observers. There is an [Observers](https://explorer.multiversx.com/nodes?type=observer) tab below the `Nodes` section.
+
+![Observers](../../media/observers.png)
+
+We can observer the same fields as the nodes, but there is no `Rating`. Why is that?
+
+Note that each Observer is only on a Shard.
+
+What should we do if we want to listen to the communication on every shard?
+
+Observer that there are other types of nodes

config.yaml

@@ -73,6 +73,7 @@ docusaurus:
                 - Transactions/: transactions.md
                 - Blockchain Validators/: validators.md
                 - Blockchain Observers/: observers.md
+                - Devnet Blockchains/: devnet_testnet.md
           - Observer:
               path: chapters/introduction/lab/content/observer
               extra: