Apple has just released iOS 11.0.2 to fix a "crackling sound" that may occur during calls on the iPhone 8 and iPhone 8 Plus. This is the second bug fix released since iOS 11 was released on September 19, 2017. The new update also fixes a bug that causes some photos to be hidden, and an issue that causes some attachments in S/MME encrypted emails not to open, according to the release notes.
Apple released iOS 11.0.1 a week after releasing iOS 11.0 to fix an issue with Microsoft email accounts not being able to connect to the server in the Mail application.
iOS 11.0.2 is just a maintenance update and does not include any new major features. The beta for the next major update has already been released to developers. iOS 11.1 includes a variety of subtle animation changes and new icons, including a new unlock animation and new Assertive Touch icons. iOS 11.1 also adds new group emoji suggestions.
You can update your supported device to iOS 11.0.2 by navigating to Settings > General > Update.