1) Default WordPress
By default, WordPress comments are activated and added to each new post or page. To disable the comments on a single post or page, go to the Dashboard to edit the post or page where you’d like to remove the comments, locate the Discussion meta box and uncheck the Allow Comments field.
If you’re not able to see the Discussion box then click Screen Options in the top right corner and check the Discussion checkbox to make it show up on the screen.
You will now see the Discussion box on the page, where you can select to turn comments & pingbacks on or off.
To globally disable comments you can go to Settings -> Discussion and change the settings there to disable the comments.
Read more on WordPress comments here:
2) Disable Comments Plugin
The easier option to globally disabling comments on your WordPress site is to install and activate the Disable Comments plugin.
Navigate to Settings -> Disable Comments to adjust the settings… This plugin nicely removes everything to do with comments on your website.