It's not clear what you are really asking. By "text" do you mean equations? The default alignment for displayed equations is centered, so that is the expected behavior. You can set the displayAlign configuration option to change that to left or right, if you prefer that (and can set displayIndent if you want a non-zero indentation). See the documentation at
for details.
If you mean how to align equations (like systems of equations, or a series of equalities), then that depends on the format you are using for equations. You don't say if you are using LaTeX or MathML (or AsciiMath). In LaTeX, you could use an align environment, and in MathML you would need to use an mtable element.
Hope that helps.
Davide