Starcraft is a game about strategy. You need to build up forces and attack frequently. This section helps newbies with how to win against the computer, or someone else via modem.
With all species, you should always get a lot of drones, SCV's, and probes. Then if you get attacked, you will have enouph minerals to build a new command center at a new spot. And one of the first things you should build is a unit building, like a spawning pool, barracks, or gateway. Then you build a lot of defense buildings around your base. At the same time as a defense is being built, build units. Build a Vespene Gas refinery. Then you can build advanced buildings and units. Also get evolution buildings, where you can upgrade units. Attack when you have at least 1 or 2 teams of units(12 per team).
With the zerg, you can build at least 3 units simultaneously, depending on how many hatcherys you have(3 larva per hatchery at a time). But you have to sacrafice a drone for each building you build. So build twice as much drones as any other species. Build a spawning pool first, then a creep colony which can evolve into a sunken colony(ground attack) or spore coloney(air attack). After the spawning pool has evolved, build atleast 12 zerglings. which isn't a lot of time, because zerglings come in pairs from 1 eggg. then build a vespene extracter. after you have at least 50 Vespene gas, build a hydralisk den. For me i get a lot of hydras, because they are so easy to build if you have enough money flowing.
After you have enough defense and units, evolve your hatchery into a lair. Then you can build even more advanced buildings and units. Build a spire and queens nest. The queens nest enables you to evolve the lair into a hive, for even more advanced buildings. build many mutas, and maybe evolve some of then into a devourer or gaurdian. Then you only need at least 2 or 3 queens. but for then to have some effect, you have to evolve their spells, like spawn broodlings. And once you have a steady team, you should attack. You need a lot of zerg units to over power the terran or protoss, because the zerg are weak compared to them.
The Terran are more powerful than the zerg, but not as powerful as the protoss. You need many SCV's to establish a wealthy base, and you need to expand to other places with minerals, because the terran require a lot of space. Build at least 2 barracks, because you get 2 times the marines/firebats/ghosts/or medics. And it speeds up the training of each. Get marines first, and build an academy to be able to build firebats and medics. Then in the academy, i always research the stim packs, because it makes the marines be able to stand up to the protoss zealots. Build bunkers all around you base, and put marines in each of them, to make the usefull. Build a vespene refinery and get some scvs inside it to harvest gas. then build a Factory, then a machine shop addon.
The machine shop addon enables the construction of siege tanks, by the way, get some of those. Research the siege mode for the siege tanks. Build Starports and wraiths, if the enemy is attacking with scouts,mutas, or gaurdians, get some valkyries. And when you have a big enough team, with some variety to it, attack. You to need as much units as the Zerg.
These bad boys are the mack daddies of the 3 species. They are the strongest, but it takes longer to establish a base and units. Once again get lots of probes. Build a Gateway. And build some cannons, for detectors and air defense. Build a lot of zealots, that should hold you off untill the enemies attack with air units. Then get some dragoons after you have built a cybernetics core, with a vespene assilimater. These species do not need a lot of units to over power zerg, and maybe a little more to kill the terran. after you have enough dragoons to fend off air units, get some dark templars. and if you are madley in control, some dark templars and mind control some drones or scvs. The dark templars are cloaked, so chances are, the terran won't see them, unless they have sci vessels or missle turrets. The zerg probably will see you because the overlords, that you must have to be able to build units, are