Mosaico extension uses
Welcome to Stack Exchange OSRT!  Yes, you can use Mosaico for designing newsletters. Whether it is easy to use is a matter of opinion, but probably most would agree it's pretty straightforward.  You create your newsletter within CiviCRM using the Mosaico extension and then send it out from there.

The main CiviCRM demo sites are not using that extension, but you can watch a quick demo of Mosaico itself and try it on the Mosaico site.  Note that the way Mosaico is used within Civi is slightly different but the basic use is the same.

You will also need to configure your system to send email.