We just went through this, but you didn't see it because the original poster also had a similarly non-descript subject name: "Hello,every body,can u help me ?" at
http://www.6502.org/forum/viewtopic.php?t=802 . So right now we have three of these in a row here under Programming.
We're not in the habit of doing people's homework for them, but we'll be glad to try to help you understand what you need to do. The other thread tells about actually keeping time.
But even with a simulator, there must be some hardware that you're simulating; and what that hardware is will partly determine how you're going to display the time and message. When I took that first 6502 class almost 25 years ago, we had AIM-65's in the classroom, and they had a routine in their ROM called OUTCH (for "OUTput CHaracter") that took care of figuring out which LED segments to light up and which character position in the display was available next and so on. I believe other computers also had a routine with the same name. To start a new line, we would just put the <CR> character ($0D) in A and do JSR OUTCH; and then each new character we would add to the line again required putting the character (its ASCII value) in A and calling OUTCH. If you're not simulating existing hardware and accompanying firmware, you'll have to write OUTCH or its equivalent too, but new students are usually given a set of these basics ready-made so they don't have to understand so much before seeing meaningful results the first time. (That was extra valuable on the AIM-65 when it came to the built-in printer, since making a mistake in telling it how to print could easily burn the print head. Obviously the school would rather have us do that part of our learning at someone else's expense.)
If you have more-specific questions with some information on what you have to work with, we can give more-specific help.