At home I had to use;
<span class="maintext">Text</span> to make my class items work.
At school, I'm on Macs. What tags do I need to use to make it work?
<class="maintext">Text</span>
If possible can we use one to make life easier?

The code is the same for every computer, there is just a difference between browsers

by using divs you should be ok

<div class="ssfd"></div>

both SPAN and DIV are usable to you.
SPAN will affect a small area.
DIV will affect a block of area (kinda like a Paragraph P area).

Thanks for that, but I still have other problems. I'm not quite sure why the other was moved to CSS.. I'll post soon.