All computer operating systems have updates which get released by manufacturers like Apple and Microsoft. The many distributions of Linux have the same situation. Computer operating systems have update services which seek out these updates on the internet and download and install them. These updates improve security and robustness of the OS.
Some updates will require the OS to be restarted to install and work properly. Others don’t need a restart. Linux is the same way – some do and some don’t. The thing i like about Linux is if it does need restarting it lets the user do it. It won’t reboot on it’s own.