According to the release announcement, Chrome 74.0.3729.108 fixes thirty-nine security vulnerabilities. The full change log lists almost fourteen thousand changes in all. Good luck absorbing all that information.
Chrome generally keeps itself up to date whether you want it to or not, which is arguably a good thing, given that a lot of malware makes its way onto computers via unpatched security holes in web browsers. You can check which version you’re currently running, and — if an update is available — trigger the update process by navigating Chrome’s ‘three dot’ menu to
About Google Chrome.