SCV is the unit responsible for gathering minerals and vespene gas as well as construction and repair of terran buildings. SCVs, while capable of completing a set of different tasks, (like a resource gathering unit from any of the three races) are not generally suitable for combat. SCV units can still be used to attack enemy units, however they are not very good at inflicting damage. They are usually a common target during a rush and therefore require protection from marine infantry units. To protect your SCV units against an early rush, build a bunker (or two) near the minerals on one or both sides of the base. This tactic will not only protect the terran base from an early zerg rush, but also can prevent early air attacks on the SCVs that are usually initiated from the back of your terran base.

One of the many advantages of the terran race is the ability of the SCV to build structures on any surface. In comparison, Zerg can only build on the creep, while protoss can only build within the presence of an energy field created by pylons.

Why SCV rush is not a good multiplayer strategy

Starcraft 2 is a well balanced game. As a Starcraft 2 player, your goal is to rank up higher in your league and eventually reach the level of the professional league players. SCV rush is a non-effective strategy against seasoned players because they are usually prepared for rushes and know how to counter an SCV rush with base defense structures, army units and basic knowledge of army control. Waiting for SCVs to reach the enemy's base takes a relatively long time. It is generally a strategy used by inexperienced players with little understanding of the game. This strategy becomes less relevant the higher you rank in the game, which is why it is commonly used by amateur players.

Quick Guide: SCV Tips and Strategies
• SCVs are used for gathering resources, repairing other units and building structures.
• Assign a few SCVs to follow your mechanical units and they will begin to repair nearby damaged units automatically.
• When under attack, SCVs last longer than a resource gathering unit from any other race.
• Double click on an SCV. If at the bottom of your screen you see 3 full rows of SCVs selected, then you have enough for a healthy economy.
• Don't let your SCVs stand unattended, always use them to gather minerals or repair structures.
• Only assign 3 SCVs to a single vespene geyser, this will produce optimal vespene economy. An exception to this rule is when your Command Center building is located far from your vespene refinery.
• Use a single SCV in the beginning of the game to discover location of the enemy base.

The marines are past criminals turned into war machines by the Confederacy. Their heavy armor allows them to withstand attacks by a wide variety of enemy units. Marines are the light infantry units. They are commonly used in small numbers as the first method of defense in the beginning of an online multiplayer match, and in large quantities later in the game. Marines carry a C-14 Impaler Gauss Rifle and can be upgraded with a combat shield and stimpack ability(which enables them to increase the fire rate at expense of fractional damage to the unit when applied).They are excellent at defending against enemy air units and zergling rushes, especially when grouped in bunkers.

Quick Guide: Marine Tips and Strategies
• Marines can attack both ground and air units.
• Marines are cheap and have a fast production period of just 25 seconds, but they are fragile and should be used in groups only.
• Group marines and other units such as Marauders, Hellions, Siege Tanks, Medivacs, etc.
• Can benefit from an increased fire range distance by going into upgraded bunkers.
• Marines are vulnerable to splash damage from units like Zerg's Banelings, Protoss' Colossi, Psi Storm, Siege Tanks, and others.

Marauders are like walking tanks that can use grenades and flamethrowers. Marauders are built on top of the firebat's CMC-400 Powered Combat Suit from the expansion of the original Starcraft game, Brood War. The common knowledge is that they were added as support units in order to increase the ability to fight zerg units. Their grenades have the function of slowing down and destroying groups of enemy units, but they are also very effective against enemy building structures, as well as heavy armored units.

Quick Guide: Marine Tips and Strategies
• Can attack ground units only.
• Use marauders as a supporting units to Marines, Hellions and Siege Tanks.