how do you ad a pic or gif  to your reply or post? 

official idiot

    and then, what are the limits to conform to?

You have to have the URL of the image you want to display.  Then, when you're typing in your reply, put in the HTML tag [IMG.] without the period followed by the URL (http-whatever) and close it out with [/IMG.] again without the period.  The whole thing has to be on one line - no line returns between parts.

I don't know what the upper limit on size is but I try not to post things that are physically too big (so that people don't have to scroll to see the whole thing) or too large in bytes (so it takes a long time to download).

Hope this helps...