Lost in "fonts" topic

Hello,

Could someone please explain how exactly do I deal with the fonts? In this topic: https://teamtreehouse.com/community/fontface-vs-link-href-google-fonts

Adam said that I need to use @font-face only when i have fonts on my computer

And in my understanding, if you declare a font in html using <link href=""> than You dont need to declare it in @font-face, you just use it thru font-family is that correct? I dont quite understand what Steven meant in this topic

https://teamtreehouse.com/community/fontface-still-viable-in-2018

"You might be using a "link" to load in a stylesheet for a font, but if you look at that stylesheet, you will find that it contains "@font-face" to actually load the font."

im on google fonts looking at https://fonts.google.com/specimen/Liu+Jian+Mao+Cao?selection.family=Liu+Jian+Mao+Cao and i cannot see anything about @font-face only the link to html and css and some @import which im net familiar with yet.

Also I have downloaded some fonts from fontsquirrel.com and most of them are in OTF format and contain a lot of otf files which i dont no what to do with. There was nothing about this file type in the course. There are some TTF, but does it mean there are only fonts for Android and IOS, and i cannot use them on desktop?

Also if I download the font, and declare it thru @font-face and will link the files properly than this font will be automatically downloaded by anyone who visits my site? Will the person be able to see what i see ?

Thanks in advance for breaking this process down for me. Konrad