.... The first thing you should do is update your system. To do that go: Apple menu () > About This Mac > Software Update. Also upgrade your OS to the latest version to have a more secure OS. macOS upgrades are usually free so you might as well keep your machine up to date. If this is a new computer there are a couple tweaks you could make to the System Preferences. These settings are all optional, consider them suggestions. Always choose the setting that makes the most sense to you.