Add gas docs to EVM

evm/10_quick-start/01_introduction.md

@@ -1,15 +1,13 @@
 ---
 title: Introduction
---- 
-
-Take advantage of the EOS Network's high throughput and low latency by deploying and running 
-smart contracts written for the EVM on the EOS Network.
-
-## Overview
+---
 
 EOS EVM is a fully compatible Ethereum Virtual Machine (EVM) that runs on the EOS Network. This opens
 up the EOS Network to the entire Ethereum developer community and tooling.
 
+You can now take advantage of the EOS Network's high throughput and low latency by deploying and running 
+smart contracts written for the EVM on the EOS Network.
+
 ## Features
 
 - Fully compatible with the Ethereum Virtual Machine (EVM)

evm/15_core-concepts/02_gas.md

@@ -0,0 +1,16 @@
+---
+title: Gas
+---
+
+In an EVM, **gas** is the unit of measurement for the amount of work that a transaction or contract execution requires.
+Every transaction that modifies the state of the blockchain must pay a fee in gas.
+
+Each operation (or `opcode`) has a fixed gas cost. You can see a list of all of the `opcodes` and their gas costs
+on [EVM Codes](https://www.evm.codes/).
+
+- The gas **required** is the sum of the gas costs of all `opcodes` that it performs.
+- The gas **fee** is calculated by multiplying the amount of gas required by the current gas price.
+
+If the transaction runs out of gas before it completes, then the transaction will fail and all changes will be reverted,
+but the gas spent will not be refunded.
+

evm/15_core-concepts/index.md

@@ -0,0 +1,4 @@
+---
+title: Core Concepts
+sidebar_class_name: sidebarhidden
+---