Since Google Chrome's version 51, Chromecast functionality is available in the Chrome Tools Menu
click the Chrome  in the top right corner of your Chrome browser window. Then click Cast…:

Cast from Chrome

Chromecast functionality is also available when right clicking on a webpage in the Chrome browser (Control+click on Mac.)

Note: To access Chromecast functionality via the the Cast button in your Chrome toolbar, you must pin the Cast button to your Chrome toolbar.

If you have more doubts, we recommend you to follow this link.