Many forums like this one use 'emoticons' or 'smileys' to add nuance and flavour to messages.
Emoticons are those little icon-like things that convey expressions. Some of them are even animated. They can be surprisingly useful on forums like this where you can't see a writer's face, hear his/her tone of voice, or know of he/she's just had half a bottle of loony-juice.
For example, if I posted in a reply to something you'd just written, "You're totally mad!" you'd have no idea if I was being serious, insulting, or pizzled.
However if I posted, "You're totally mad!"  you'd instantly know I was joking with you.
On the other hand, "You're totally mad!"  should have you coming after me with a pointy stick, because I'm being a rude moron with the debating skills of a club hammer!
Or, when you've just read an apparently terse reply to something you've posted, how d'you react? Then, how do they say, "Sorry"?
Smileys or Emoticons are just tiny images - the animated ones are in a format called .GIF and all you need to do to use one is right click on it to bring up the context menu, select 'copy image' with the left mouse button, then paste it into the appropriate position in your post using the same context menu but this time selecting 'paste'.
Yes it's often juvenile and, as we've seen. some people can even find them annoying (it's beats me why - but life's a rich tapestry and all that....). But, as a conversational safety-valve, I've found them a valuable tool .... especially if dealing with members who are bigger than me.
Are these a good idea in your opinion? 
here's a selection I've bunged into a spare webpage for you to look at.................. View a smileybank