Ok, I downloade the Ghost Marine just because I wanted to see what hapened because this is my first time here. Is there some kind of loader you need to use these units, because nothing happend after I downloaded it. Please just include how to make these units actually show up on SC after downloading them.

What is the ghost marine? Welcome to the forum.
Are you using staredit? You have to use scmdraft 2 or starforge to view it.

I'm not sure I understand exactly what the problem is - but if you downloaded a map and are wondering why it's not doing what it's supposed to do when you play it, you should try setting the game to a "Use Map Settings" game from the little drop down menu above the section where you select your race. If that's not what you mean, the please clarify the issue.

Where would I get scmdraft 2 or starforge.

Here you go.

He's talking about this http://www.staredit.net/files/423/

It is a grp file which means that only has the graphics for the marine. It can be included into a mod and then the mod can be played to change the marine graphics. But you'll be the only one that sees the new marines over battle.net.
Anyway is quite complex, so if you're new I'd stay away from mods until you know some stuff.

So what do u suppose I do? Download SCM Draft and mess around with it for a while?

SCMdraft is an extended map editor, which is used to create maps with features that can't be done with the normal staredit. It has nothing to do with modding. As Clokr_ stated, you shouldn't bother your head with modding yet.

So, what should I do?
Other than anything that has to do with modding.

You should start mapping

Just learn the triggers and general terrain first, then start getting into the extended terrain. Then try making actually maps.

I'm still working on the extended terrain part o.O

I have some experience with mapping and triggers. And have made 1 game before, it wasnt an online game but it used a whole lot of trigger, so it wasnt just some player vs comp regular game or anything. This was with the normal SC campaign editor though, should I download SCM Draft to get more experience?

Thats up to you. When you're ready to learn more then yes, dl it and browse the forum and wiki for some cool stuff.

I would get SCMDraft and look at some of the terrain stuff here, then get an idea and try to do something like it.

Here's some good Stuff.

Reference
Tutorials
More Tutorials

I might as well introduce you to Falkoner's website, because he's going to do it anyway. Linky.

You can make a great map in regular StarEdit, too. Many many many classic maps have been made using just StarEdit, and it's a lot easier to start out that way, I think. SCMDraft can be kind of confusing to start out on, with so many unused and extended features, it's hard to know where to start. StarEdit lays out all the essential tools very simply so you can learn to use them, then if you start to want more, you'll appreciate the need for SCMDraft and be able to reproduce exactly what you want. That's what I'd do, but it's up to you.

Lol, I actually looked at this topic, but thanks You're going to eventually end up using SCM Draft for everything, so you might as well start now.

That's not true... I don't use it.

Farty: Always the exception