Most of time, the text in forums discussions is aligned on the left, but you can change the alignment in your posts, for decoration, when submitting in some language that's written from right to left, or for any other reason.
There are three tags for text alignment:
[left] - Text left aligned.
[center] - Text centered.
[right] - Text right aligned.
The tags are applied to text as with other tags, they have to wrap the part of your text you want to change the alignment (read How to Correctly Insert Tags).
[left]This text is left-aligned.[/left]
[center]This text is centered.[/center]
[right]This text is right-aligned.[/right]
In order, the three lines above will look in your final message:
This text is left-aligned.
This text is centered.
This text is right-aligned.
What to add? Hmm ..
1. That it's useless to combine two or all three alignment tags, that would only help to get an undesired result (more about combining tags HERE).
2. As with Fonts Change, the guys from phpBB think it's useless to let users align text as they wish, let's hope they fix that soon. With other popular forums platforms text alignment works fine: vBulletin, IP.Board & Simple Machines.
3. If you're not sure what software the forum you're part of uses read: What Kind of Forum are You Using?
4. Click here to know how to align pictures.