ok least take this in baby steps

I want to change my text in the main body
to be centered at the top
stylesheet text I changed to this :
/*The main content classes*/
#contentColumnMain, #navColumnOne, #navColumnTwo, .centerBoxContents, .specialsListBoxContents, .categoryListBoxContents, .additionalImages, .centerBoxContentsSpecials, .centerBoxContentsAlsoPurch, .centerBoxContentsFeatured, .centerBoxContentsNew, .alert {
vertical-align: top;
text-align: center;
font-family: comic sans Ms;

also when I want to change individual font size within an area I assume I do this with my html coding in languages?TIA