Download the chromecast extension for Chrome and it will put an icon on the right side of your address bar allowing you to cast specific tabs etc.
Also, when watching YouTube or Netflix, there will be an icon underneath the videos you're watching which will let you choose whether you want to watch on your TV or the PC.
Also download the app on Play and you'll be able to cast via your phone.
We've a load of info in our resources sticky if you want to take a look.