the <font> tag

I am going to say very little about this tag because its use is frowned on and in newer versions of html its use is "deprecated". So, if you can avoid using it, do so.

The reason its use is frowned on is because it lets the designer shy away from using tags as they should be used. It is better to use the body attributes color, link and so on; or use styles.

But, because you will use the font tag, here's a bit about it.

Note: Programs that convert a word processed document to a html document may insert a large number of font tags. Some html editors have tools that can remove these untidy font tags. The result is a smaller file that loads much more quickly.

Never use the font tag when you should use the heading tags

the attributes

color          as for the body tag

face           a comma separated list of font 
               names not all operating systems 
               have the same fonts, so you need 
               to cater for several possibilities
               example: face="arial, helvetica, 
               verdana, sans-serif"
               These four fonts are all similar in 
               appearance, but are found on the 
               different operating systems. The 
               browser uses the first one it can. 

size           Font sizes in web pages are relative. 
               So font sizes are set by specifying 
               a number +1 to +4 to make the font 
               larger or -1 to -4 to make it smaller.
               Or you can set the absolute size by 
               specifying a number from 1 to 7.

This is an example of using the font tag to make the text larger and larger and then smaller and smaller covering the full possible range.