According to the release announcement for Chrome 70.0.3538.110, the new version fixes a single, High-severity security vulnerability. The change log lists a few additional bug fixes but nothing particularly interesting.
Chrome will update itself automatically on most computers, over the next few days or weeks. If that’s not soon enough for you, click the browser’s menu button at the top right (three vertical dots) and drill down to
About Google Chrome. This will show your current version and — usually — offer to install the latest version.