If you have a wordpress website and don't need to allow the visitors to comment on your pages, posts and custom types, then you will need to install a plugin, click a few settings and you are done!
Do I need comments?
First of all, you should ask this question about your site, do you really need comments? For instance, if your site is only providing static information on pages and does not let's say have a blog in it, then maybe you don't need to allow comments.
If your site on the other hand has a blog and you write posts here and there, then probably allowing comments would be a good thing to have.
So if you don't want any comments at all on your site, you can download and install or find and install via the plugins browser in your wordpress website, this plugin called "Disable Comments".
Once you install this plugin, you can then go to Settings -> Disable Comments and enable the plugin, check to permanently and persistently disable comments on the site. This way you can also avoid SPAM.
What are my alternatives if I do want comments to be ok?
Multiple. You can use DISQUS or wordpress's native commenting system ( which will also at some point force you to enable Akismet also for handling SPAM ) or even Google+ as your comment-management system. You can also have your comments be handled by Facebook's commenting plugin. To our knowledge and preference, DISQUS is a very good one.