Every single month Google publishes a new security patch for the Android operating system and begins pushing out the updates to the list of supported Nexus devices, while other OEMs grab the software and push the security patch themselves, and only two days into the month Google has already posted the factory images for the May Android Security patch. With factory images now live, those who are interested in getting the latest software on their device can flash the factory images, allowing them to sidestep the waiting period for Google to push the software out to devices and get it running on their own device immediately, so long as they have the needed tools to get the job done which includes the fastboot tool and the latest version of the Android SDK Platform Tools.
At this point in time, the changelog for May's security patch is not yet live so there isn't any detail on what security fixes are coming to devices with this update. Having said that the changelogs for these patches usually aren't too far behind. If you're unfamiliar with flashing the factory images to your device, it's likely a better idea to wait for Google to simply push the software to your smartphone or tablet over-the-air, and although this could take days, it's a safer option than first-time flashing if you're uncomfortable with it.
There will also be opportunities to flash the OTA files once they start hitting devices and the links to download the OTA directly are published to the web, if you prefer to flash the OTA file instead of the factory image. Right now there are factory images up for the Pixel C tablet, the Nexus 6P, the Nexus 5X, the Nexus 6, the Nexus Player, the Nexus 9 tablet in both WiFi and LTE models, the Nexus 5, and the Nexus 7 2013 in both WiFi and cellular models. If you have any of the supported devices listed here, you can head to the factory image page from the source link below and pick up the corresponding factory image download, which is still Android 6.0.1, but that should be a given as this is only a security patch.