Navigating the web platform

MDN Web Docs is a comprehensive standards web development resource for web developers. It provides documentation and compatibility information on all web technologies, including HTML, CSS, JavaScript, SVG, and APIs.
Can I Use also provides browser compatibility information.

The web platform is implemented by multiple browser vendors, not just one. Individual vendors only tell you what's new in their own browsers.
Use the Web platform features explorer to stay up to date with what's new across all of the browsers.
Use BCD Watch to keep an eye on browser compatibility data changes, coming from browser updates.

Baseline features are features of the web that have reach a level of implementation maturity across all browsers that they're very safe to use. The Web platform status dashboard provides a list of features that have become Baseline each year.

Each browser vendor publishes its own release notes. Release notes are lists of bug fixes, new features, and removed features, per release of the browser.

Browser vendors announce new features and updates to their browsers on their blogs. Reading these blogs is helpful to stay up to date with what's new and what's coming next in each browser.

Browser vendors work on new features all the time. Here are a few ways to know what's coming next, and at what stage of development a feature is.
Chrome Platform Status lists new features that are being added to Chromium, the open-source project which Chrome, Edge, and many other browsers are based on (use the search input field to find a feature, learn more about it, and check its current implementation status).
Browser vendors also send Intent to prototype/ship emails when starting to work on a feature. The IntentToShip bot is a good way to keep track of what's coming next.

Mozilla and WebKit maintain standards positions repositories, where they share their point of view about new feature proposals. For example, when someone wants to add a new feature to Chromium, they usually request a position from Mozilla and WebKit about that feature.

Web Platform Tests (WPT) is a test suite project for the web, which all browser vendors contribute to. The test suite tests the interoperability of web features across browsers. Navigate through the test folders or use the search input field to find the tests for the feature you care about, and review the number of failing tests per browser.

Yearly developer surveys feed into the set of developer signals that browser vendors look at when prioritizing their efforts on the web platform. Sharing your pain points and missing features in these surveys helps browser vendors understand what developers need.

Interop is a yearly project where Apple, Bocoup, Google, Igalia, Microsoft, and Mozilla get together and focus efforts in fixing highly requested interoperability issues of the web platform. Every year, before the next iteration of the project starts, a submission window is opened for anyone to propose new focus areas. Focus areas must be about existing features that have a stable specification so browser vendors can focus on fixing inconsistencies.

Report browser engine bugs when a web feature is supposed to work a certain way but doesn't. Always try to provide a reproducible test case so that browser engineers can easily verify the problem and find a fix for it.

When you find a website which doesn't work the same way across browsers, report the issue on the Web Compat website. Knowing about the most common and most important web compatibility issues helps browser vendor prioritize the right fixes, including in the Interop project.

Use the Web We Want project to report new web feature ideas and concepts that you think browsers should implement but currently don't.

Browser vendors often need more than one release to fully implement a feature. During the early development phase, a feature is often hidden behind a flag. You can enable a feature flag in your browser to test it early and provide feedback. Participating in the development of a feature by testing it early helps browser vendors catch bugs and improve the feature before it's released to everyone.
Browser vendors also create origin trials (OT) for some features. OTs allow you to virtually enable a feature for your site only, only for the browser which the OT belongs to. This allows you to test a new feature on you production website, with your users, for example to get ready for that feature, and to provide feedback to the browser vendor.

Explainers are documents that are used to propose a solution to a web developer problem area. Explainers are useful documents used to socialize and review a new feature proposal before that feature becomes part of one or more web specification. Explainers are hosting on GitHub repositories where you can share your feedback about them.