If its for you and only you, you cannot put it into the CSS, unless you know a code to limit it only to you.
If you want it to appear in your posts then post this:
[font=Terminus]text[/font]
On second thought, how do you guys like the code?
I'll duplicate the installed theme with a new name, then change the font.
Do you like the guide though? If so give me rep

Note that this relies on a browser with a fairly up-to-date implementation of CSS3.
You can upload the font to the host
Be sure that the font you're trying to use allows such use in it's license. A lot of the commercial fonts I've seen have a special clause in the license regarding @font-face. Most free fonts don't because the unmodified license usually allows it anyway.
Re the guide - it could be a lot clearer - you are not covering older browsers either. If you want a custom font for IE6/7 then you will also need to upload the eot file.
@font-face {
/* for IE */
font-family: 'MyCustomFont';
src: url(images/font/nameoffont.eot) /* EOT file for IE */
}
@font-face {
font-family: 'MyCustomFont';
src: url(images/font/nameoffont.ttf)
}
.thead {
color: #ffffff;
font-family: 'MyCustomFont', Verdana, sans-serif;
font-size: 14px;
}
Usually, people update their browsers when new ones come out, kinda like how people upgrade after MyBB gets a new version.
Also, I didn't use a guide, I used it from my own knowledge and it works
However, I am really surprised that IE used eot files...
That is pretty outdated, considering that we dont need embedded fonts now.
Convert your TTF to EOT
here
Well people with older versions of IE can't view it because Microsoft makes things really hard for people, you see they literally MAKE you use a certain file type they invented in their programs, why? So that they can make more money for more people who make the file extension.