A lot of Starcraft mapping is pretty logical. If all the conditions of a trigger are filled, that is ALL of them, the trigger will execute its actions, in the order from top to bottom that they are listed in the trigger.
Starcraft checks every trigger for condition fulfillment roughly once per second (please correct me if I'm wrong) without hyper triggers, and roughly 12 times per second with hyper triggers.
When checking triggers, Starcraft checks in a specific order, starting with Player 1, then it goes down player 1's list, then it does player 2, then Player 3, ect. This means ORDER MATTERS.
Here's a problem a friend of mine had
Players:
Force 1
Conditions:
Force 1 brings exactly 0 men to Location 1
Force 1 brings at least 1 men to Location 2
Actions:
Give all any unit owned by Force 1 at Location 2 to Neutral
Display text for current player "blah blah w/e"
Now, this trigger runs for p1 first (assume p1-4 are Force 1)
The text is displayed for p1, the men are given to neutral
Next, when it checks this trigger for p2, FOrce 1's men have been given to neutral, so it does NOT fire for p2
and p2-4 sees no text.
Some little quirky things like that you need to look out for.
Also a beginners mistake I think is common, when you have a trigger like
Players:
Force 1
Conditions:
Switch 1 is Set.
Actions:
Create 1 Terran marine at Location 1 for Player 1
This will create 1 marine for each Player in Force 1, and all for Player 1.
Death Counts:
Starcraft keeps track of how many units of each type have died for every player, and you can also Set how many have died.
This is extremely useful in starcraft mapping since it allows you to keep track of a great deal of things.
As for a first map, I might suggest what I've personally classified as a "path" rpg. That is, you follow a defined path with a hero that either changes unit type, gets minerals, ect. There is generally a limited amount of text, basic terrain editing and the occasional "give" or "kill" or "create," units, ect. Make a few towns, think up a simple storyline, it uses all the basics. If you find that easy, add spells. If you're spells are ownage, add more stuff.
Quote from name:NerdyTerdy
If I were you I'd just play around in the editor for a couple days. Look around at all the features and try to figure out what does what. If you can't figure something out, and you can't find a tutorial about it, post here. Someone will likely know the answer.
This is also good advice.
None.