First make sure you have installed node.js 8.X and npm 5.X version. You can check it on own terminal window simply by entering node -v and npm -v. You can also download latest nodeJs from here.
$ npm -v$ node -v
Make sure you have installed ionic-cli latest release and Cordova. You can check ionic version in terminal with ionic -v command. If you need more info on how to setup ionic project please follow Ionic Getting Started at Ionic official websites.
Ionic 3 target IOS, Android, Window all these three platform so you need to install there respective SDK to make a build. Even if you didn’t have SDK configure still you can run this app in browser.