Outline
Netlify will rebuild and redeploy your site each time you push to the configured branch. So, if you selected master as the branch from which to deploy, any push to master will cause the site to rebuild and redeploy automatically.
For the exercise, change something on the site. It could be a text color, adding a new page, adding a new paragraph, or whatever you'd like. Make the change and push to your deploy branch. Check the build logs on your site info page in Netlify, and you'll see the new build there. When it's done, reload your site and see your change.