To make your letter bold use ** ** without gap.
Example My name is wajahat sardar
use _ _ to make your letter italic like this without a gap.
Example My steem username is @wajahatsardar

User some HTML5 mark up like this If you want that your post will be written in the center then use this < center> < /center > mark up without gap and write your paragraph between them.
Example:

Follow me at @wajahtsardar
You can also covert this into bold letters:
Example:
Follow me at @wajahatsardar

Now Center / Bold / Italic writing.
Example:

Follow me @wajahatsardar

You can do so just by combining all the markup in sequence. < center> ** _ Write your sentence then close _ ** < /center> without gap.
It is some basic of writing style I usually use in my posts.