How to use a custom font on a web page and/or mobile

My client wants to use he Comfortaa font on the website, and I suspect it is not available to everyone by default by just adding it to your CSS?

I notice that some sites that use it, import it from the fonts.googleapis.com? is that what's happening here?
<link rel="stylesheet" type="text/css" href="//fonts.googleapis.com/css?family=Comfortaa" />

But we can't do that, because our salesmen have a non-internet version that they show clients, and so it has to be available offline.

I've seen where you can download the font here:
https://www.fontsquirrel.com/fonts/comfortaa

But I don't know if that site is legit or just going to put spam and spyware on my machine.

Also, there is a download link on the right here, but I don't know if that is downloading this font or something else:
https://aajohan.deviantart.com/art/Comfortaa-font-105395949

So the question is, when there is a custom font, how does one typically get it embedded for use into their website, and even their mobile app if possible?

thoughts?

thanks!