keep the pressure on bro 
Your not going to develop good mechanics just rushing all-in every game. You need to focus on a build and go for longer games. Need to have experience in late mid game and late game. Having 3+ bases up, and everything that comes with it like teching, macroing up large armies off multiple bases, upgrading, microing with drops/splitting battles to break a contain, microing your large army, it just gets really intense later in the game you go, and a lot more fun. You just need to be able to play it. You can't cheese your way to diamond.RUSH RUSH RUSH!!! RUSH THEM! lol It's what I did...
ive done rush hundreds of times
played zerg, hated it
Protoss is a pain but fun
Terran is actually fun because i don't have to sacrifice gatherers
ive dont the divide n conquer, built up two seperate forces, attacked from one side and moved my other forces to the reverse side to take out the buildings.
ive done the Ray rush, where i build up like 20 rays and rush
ive zerg rushed and failed....horribly
Yes, scouting is 100% necessary so you can see where your opponent is on 4 player maps what he is doing so you can react. Walling off is also critical, they can get units into your base and gg you before you have units up if you don't have a wall. AI doesn't rush like that so it might not matter against them as much.I'm a terran fan, so is it very necessary build a barrack to block entry point? Is scouting necessary too? I've been training with AI for the past 3 days but still havent come up with a nice strategy. :|
Sometimes i even got owned by Easy Zerg Level! T_T
Yeah, it's really not fun if you don't wall off. 6 Zerglings run into your base, you have no units, they start destroying all your SCVs, which in the early game each one matters. Then you lose, or your a major disadvantage the whole game.
Yes, the number on the build order is your supply count. Another tip, keep making workers. Anytime you can fit them in, through the whole game.ouch, that hurts. T_T
that happened to me like... out of 10 games with zerg... 10 times... T_T
On that website, im not so familer with the terms used... like.. 3 raxx? is that barracks?
Your just lucky you didn't start off playing brood war, if sc2 has a learning curve brood war was a wall. Can only select 12 units at a time, can only select 1 building at a time, can't rally workers so you have to manually move them to the mineral patch. No smart-casting, so all your casters you selected cast all at the same time. We all learned that when we started playing when we were like 12 :/SC2's hard. Like, I practice and learn a lot of strats but I just can't seem to win. I do good usually though. Honestly I recommend this. Watch the entire series. You will learn A LOT!
http://www.youtube.com/watch?v=92Rv-s-7rNk
Husky/HD are more for entertainment, but you can still learn a lot if you watch the production tab/supply numbers.You can also learn quite a lot by watching pro players play. The best way to do this is find battlecasts on youtube.
HDStarcraft and Huskystarcraft are amazing places to start. Find their channels and just start watching games. The commentary is good and you'll learn a decent amount of stuff just ingesting what the pros do.
Scouting is absolutely essential and can make the difference between a loss and a win. On top of this, knowing how and when to harass as well as when to expand is also key.
Usually the safest time to grab an expansion is when you're doing an assault or putting harass on an enemy. They'll be too distracted to think about harassing themselves, and if you keep up with your macro (that is, your capacity to create and build things in your base) even if your assault loses, you'll have a sizable force ready to defend any expansion.
You have to try and contain your enemy. Make everything hard for them. They're getting an expansion? Punish them for it. Destroy their workers. Assault it. Make sure you have them on their toes every minute of the game, and not the opposite way.
Also make sure you have eyes all over the map. You never want to be caught off guard by a drop or a nydus worm. If you're Terran, spread your supply depots out around the corners of your base (but make sure you can defend them mid game vs air). If you're Protoss, try and do the same with Pylons. If you're Zerg, you have the best scout in the game--the Overlord.
If you know when an enemy is moving and what their composition is, you'll be readily prepared to handle it when it enters your base.
On top of all of this, get used to using control groups. That is, hotkeying your structures and army with ctrl+1 ctrl+2 and so on and so forth. Selecting a group of barracks to replenish your forces whilst in the middle of a battle can make all the difference when you have to push with reinforcements.
There are many more tricks of the trade to learn, but those are the simplest. Map control. Containment. Knowledge of your opponent.
Play and play and play some more. And then watch replays. Watch a LOT of replays. You can never learn enough.
That's all I can really say.