Welcome Arolds. The Campaign Editor comes with your Starcraft game. Just go to Programs-> StarCraft->Starcraft Campaign Editor and start with that. There are other editors, but if you're new to this, you might want to just stick to this one for now. Others are not neccessary for making a good map, although they have their uses.
You only need other editors for stuff like custom terrain like wider ramps, ramps in other directions than staredit allows or stuff like that. I would not recommend doing them at the beginning, it's very time consuming and does not make a bad map good anyway.
Another program you need is scmtojpg, look in our filebase. This helps in making pictures of your map to upload here. Also you should understand that it is all about "melee" maps here, so no maps that need triggers to work and have to be played "use map setting". Read our articles!
yeah.. i have already done some maps since i had started playing, but i think they suck hehehe
but for now, ill try to learn about map making.. and later do some good maps.. who knows? ehe
sorry all for the poor english and thanks for the attention =)