If you want to use the "Arial" font for a block of text, all you have to do is surround it with FONT FACE tags:
<FONT FACE="Arial">This is in Arial font</FONT>
This is Arial font
Of course, not all the computers are going to have the type of font you want your text to use. FONT FACE tags will let you specify more than one font face, so in case one font face is not available, browser will use the next available font face:
<FONT FACE="Garamond,Helvetica,Times">Hi!</FONT>