Hi5 Question Please.. [writing]?

Ok.. so I dunno how to say this but some people when sending comments, the writing is different. They sometimes make it bold or @ d centre or in italics. Even in the 'about me' section.. they make it look so cool. Do u have any idea on what site I have to go or if I have to download a software? Thanks.. And sry but I'm rly bad at explaining stuff =D