Reload VS Code after the installation (click the reload button next to the extension).
Open your desired GitHub repository.
If you're using version 0.5.0 of the extension or higher, a new viewlet should be added to the bottom of the activity bar. For older versions, the GitHub Pull Requests treeview will appear in the SCM Viewlet.
You may need to configure the githubPullRequests.remotes setting, by default the extension will look for PRs for origin and upstream. If you have different remotes, add them to the remotes list.
A notification should appear asking you to sign in to GitHub; follow the directions to authenticate.
You should be good to go!
This extension is still in development, so please refer to our issue tracker for known issues, and please contribute with additional information if you encounter an issue yourself.