Instructions
Order your probes to gather minerals, and create additional probes at your Nexus. The majority of your probes initially should be sent to gather the crystals.
Order a probe to construct a Gateway within range of a Pylon field. Once completed, the Gateway can produce the most basic Protoss offensive units.
Order the same probe to create photon cannons at defensive positions around your base. Two or three of these cannons at each entrance will prevent enemy units from penetrating your base long enough for your forces to assist. Cannons must be powered by a Pylon structure.
Create research buildings like the Forge, and use them to upgrade your units and structures.
Build more advanced structures as you acquire the resources to do so. Bolster your forces with stronger units from the Robotics Facility and the Stargate. Carriers and Colossi are both extremely powerful units.
Use your amassed forces to complete whatever objectives you might have.