In ACP > Manage > Privileges, select the category you want to allow guests to post in, and give guests the "Create Topics" and "Reply to Topics" privileges.
How create a table like this post? and how center etc?
| Tables | Are | Cool | | ------------- |:-------------:| -----:| | col 3 is | right-aligned | $1600 | | col 2 is | centered | $12 | | zebra stripes | are neat | $1 |
Maybe this site would be useful http://www.tablesgenerator.com/markdown_tables
Nice! and what about text align?
|No way to center out of tables?|
I don't know any way and it would surprise me if there was since it's an aim of Markdown to get rid of bad markup.
What does justify text to be centered? Mostly you do this for some kind of header-text, use
##, etc. for this.
Maybe you want to use it as some kind of footer, use
hr) for the separation.
Centered text is just meant for esthetic reasons but the text doesn't really have a justification for this, so Markdown doesn't support such usage in order to keep a clean standard.
If it's images you want to be aligned centered I can understand your sense of esthetic. But you still need the admins help to allow this (e.g. using this hack).