Awesome

PhpStorm Magento 2 Plugin

Go to Settings > Preferences in the PhpStorm IDE
Navigate to Plugins
Click the Browse repositories... button and search for "Magento PhpStorm"
Install the plugin and restart PhpStorm
Go to Settings > Preferences > Languages & Frameworks > PHP > Frameworks > Magento in the PhpStorm IDE
Check Enable and click the OK button

Configuration smart completion and references for XML/JavaScript files
Navigate to configuration reference in scope of class/interface
Go to plugin reference in scope of class/interface and method
Navigate to Web API configuration reference in scope of class/interface and method
Plugin class methods generation
Plugin declaration inspection
RequireJS reference navigation and completion
MFTF reference navigation and completion
GraphQL navigation line markers
Code generation
Inspections for XML configuration

Check out this repository
Open a folder with the project in the IntelliJ Ultimate using the open action button.
Make sure that you on the latest develop branch (e.g 5.1.1-develop)
Right-click on the build.gradle file, choose "Import Gradle project" (if this is not exist look for "Build module '<root folder name>'") (you need to have Gradle plugin installed)
Check if the right SDK version is used for the project.
- Current Java version for the project is java 11, so you should additionally download SDK 11 and choose it in the module settings: Right click by the project root > Open Module Settings > Project Settings > Project > Project SDK
- Check if right SDK version is used for the Gradle plugin: Intellij IDEA > Preferences... > Build, Execution, Deployment > Build Tools > Gradle > Gradle JVM and choose your JDK.
When the Gradle sections appeared in the right bar, navigate there and right-click magento-2-php-storm-plugin > Tasks -> Intellij -> runIde
Click Run "magento-2-php-storm-plugin" to run the plugin. You should see a new instance of IntelliJ launched with the plugin installed. Make sure the plugin is enabled in IntelliJ settings and indexing is finished. Plugin features should be accessible at this point.

Start with looking into Community Backlog. Any ticket in Ready for Development and Good First Issue columns are a good candidates to start.
Didn't satisfy your requirements? Create a new issue. It can be for example:
- Bug report - Found a bug in the code? Let us know!
- Enhancement - Know how to improve existing functionality? Open an issue describe how to enhance the plugin.
- New feature proposal - Know how to make a killer feature? Do not hesitate to submit your proposal.
The issue will appear in the Ready for Grooming column of the Community Backlog. Once it will be discussed and approved the issue will be ready for development.
Refer to the Contributing Guide for more information on how to contribute.

Create sandbox folder
Copy to sandbox folder composer.json and composer.lock
In sandbox folder create app/code and vendor/magento
Copy any of the magento modules (as for example: framework, module-catalog, module-checkout, module-customer, module-sales) into the vendor/magento folder. It is better to add as few modules as possible to reduce reindexing time during application running
(Nice to have) Open IDE and go to Preferences > Editor > File and Code Templates > Includes tab and add default headers for PHP File Header and XML File Header

PHP File Header:

/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
declare(strict_types=1);

XML File Header:

<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->

Each Magento source file included in this distribution is licensed under OSL-3.0 license.