I have never played an RTS : o. Which game, that is on GOG, should I start with?

BTW, this was supposed to be a question how do i edit it?

Total Annihilation is an awesome RTS, I'd start with that one

thanks ill check it out.

There are still a ton of RTS's not on GoG that are worth playing, but there's Age of Wonders, Empire Earth, and as already stated, Total Annhilation.

I'd also recommend Command & Conquer, Homeworld, and Starcraft.

Total Annihilation is indeed a good start - and it also lets you see how utterly epic an RTS game can be.
Also, I agree that you could ckeck out Empire Earth; the first one is a solid game with everything you may need for an RTS. Personall, I prefer the second one, but it might be a bit too customizable for a newcomer.

If you'd like a less standard game advice, go for Sacrifice. It's a fun and hilarious game with a very unique scope.

On GOG? Ground Control 2.

Not on GOG... Starcraft / Warcraft / Company of Heroes. ;)

Homeworld (not on GOG yet, maybe this summer with EA)
Ground Control (the first is better but that's more like tactics)
Sacrifice

Ohh, and I almost forgot: Dungeon Keeper

EA would have nothing to do with getting Homeworld I don't think. I was developed by Relic, who are owned by THQ (not on gog) and was published by Sierra (owned by Activision). So gog would have to one sign THQ, then work something out with them and Activision.

I am going to second the Total Annihilation recommendation. It contains most of the mechanics that are typical in even more modern RTS games and should give you a great indication of whether or not the genre is for you.

Don't Forget Rise of Nations!

not available here but an awesome game none the less.

Well, if you want to try an RTS without having to buy one, try Warzone 2100:

http://wz2100.net/

It's open source now, completely free.

Yeah, you should play Original war after other RTS, because it is the best and so alone. :(