Create/specify those in your stylesheet (CSS) file.
For example, here’s the CSS I use in a blog entry:
.entry {
font-size: 75%;
line-height:150%;
padding-bottom:25px;
padding-left:20px;
padding-right:20px;
text-align:justify;
}
The last line specifies the justified the text.
The CSS is referenced in the weblog multi-entry template:
<div class="entry">
<h2><a href="%%comments_url%%">%%title%%</a></h2>
<p class="entrydate">%%date%%</p>
%%blurb%%%%body%%%%more_link%%
<div class="author">%%comments_link%% <a href="%%comment_permalink%%">permalink</a> | Category:%%category%% </div>
</div>
Once in a while if I want something centered I’ll just do this kind of thing on the fly in the blog entry:
<div align="center">text here</div>
You could put that code into one of the unused formatting buttons.