Wait wait, loveyou is making too much confusion.
A teeworlds server, for working, need to listen for client on a UDP port. If you want more than one server you need to have one port each server. For example
SERVER 1: sv_port 8303
SERVER 2: sv_port 8304
By the way sometimes your modem/router is not configured to accept incoming connections and you can't host a server. In that case you will read in the console a text saying you "CAN'T CONTACT THE MASTERSERVER". If you are expreriencing that problem you need to portforward your router and I suggest you to read the modem manual or to google it.
The MOTD, or Message of the Game, is a Teeworlds feature and got nothing related to the netcode we discussed until now. It's a message that appears to the client and display informations on the server. I understood only now, after this:
loveyou wrote:Wow rapid answer! Thanks!
but the black board its the server where there is all the information.... If i want to open my server i click on it and it appear a black board.
That with "blackboard" you mean the DOS or console window, not the MOTD. Sorry for the mistake. The answer to your question is YES, you need to leave it opened to host a server. If you close it the server die.
Support Staff - ESL.eu Teeworlds Admin