Allies
The Allies use the build system traditional to Command and Conquer. When a building is selected to be built at the ConYard, it is built up over time and then when deployed, it is instantly ready to use. They do not give ground control however, so you will need to expand your base by relocating your MCV or deploying Prospectors into Command Hubs.
To use higher tier units deploy your MCV or Prospectors near your Boot Camps, Seaports, Armor Facilities and Airbases and upgrade them to maximum clearance.
The Allies have big ground control when it comes to deploying their MCVs and Prospectors.
Soviets
The Soviets build up their structures on the map. While being built they are unusable yet vulnerable. When finished they can expand ground control. The Soviets can also build a Crusher Crane to unlock a second build queue.
To build Tier 2 units and structures build a Super Reactor and to build Tier 3 units and structures like the Vacuum Imploder build a Battle Lab.
Like the Allies the Soviets may use some units to deploy Sputniks to expand ground control but Sputniks provide smaller Ground control than Prospectors.
Empire
The Empire's build system is very unique. Structures come out in the form of Nanocores, which can traverse both land and water. They can unpack into structures anywhere on the map. This system is good for grabbing Ore Nodes quickly. The Nanocores are vulnerable to attack however, so escort them with Tsunami Tanks and Mecha Tengus.
A major drawback to Nanocores are that they build up structures slow and they provide small ground control(for Walls).